^ 





COPYRIGHT DEPOSIT. 



J 



STEAM-BOILERS 



BY 

CECIL H. PEABODY and EDWARD F. MILLER 

Professor of Naval Architecture Professor of Steam 

and Marine Engineering Engineering 

Massachusetts Institute of Technology 



SECOND EDITION, 1904 

AND 

THIRD EDITION, IQI2 
BOTH REVISED AND ENLARGED BY 

EDWARD F. MILLER 

TOTAL ISSUE, ELEVEN THOUSAND 



NEW YORK 

JOHN WILEY & SONS 

London: CHAPMAN & HALL, Limited 

1912 



Copyright, 1807, 1908, 1912, 

BY 

C. H. PEABODY and E. F. MILLER 



I* 



3 




Stanbopc jpress 

F. H.GILSON COMPANY 
BOSTON, U.S.A. 






PREFACE TO THIRD EDITION 



In this book as revised we have attempted to give a clear and 
concise statement of facts concerning boilers and their auxilia- 
ries, and of the methods of designing, building, setting, manag- 
ing, and caring for boilers. 

The subjects of mechanical stokers, economizers, and steam 
piping have been treated at considerable length, and the use and 
calculation of induced draught fans quite fully explained. Much 
new material on chimney draught, the result of work extending 
over a period of years, has been added, as has also a chapter on 
coal handling and coal-handling machinery. 

Nearly every chapter has been enlarged and the number of 
illustrations more than doubled. 

The chapter on combustion has been extended to cover oil 
burning and to include the most recent analyses of American 
coals, together with a detailed description of coal calorimetry as 
applied to the determination of the heating value of coal pur- 
chased on a " heat unit " basis. 

The chapters on staying riveted joints and boiler testing have 
each been extended. 

While the book was planned primarily for the use of students 
in technical schools, and in the two revisions has been increased 
so as to meet the needs of the students at the Massachusetts 
Institute of Technology, it is felt that the book may prove useful 
to engineers in general. 

C. H. P. and E. F. M. 

September i, 191 2. 



CONTENTS. 



CHAPTER I. 

PAGE 

Types of Boilers i 



CHAPTER II. 

Superheaters 37 

CHAPTER III. 
Fuels and Combustion 48 

CHAPTER IV. 

Corrosion and Incrustation 103 



CHAPTER V. 

Settings, Furnaces, Chimneys, Economizers, Mechanical Stokers, and 

Induced Draught Fans 129 



CHAPTER VI. 
Power of Boilers 213 

CHAPTER VII. 
Staying and Other Details 223 

CHAPTER VIII. 

Strength of Boilers 249 

v 





VI CONTENTS. 

CHAPTER IX. 

PAGE 

Boiler Accessories 326 

CHAPTER X. 

Coal Handling and Coal-handling Machinery 383 

CHAPTER XI. 

Shop-practice 408 

CHAPTER XII. 

Boiler-testing 437 

CHAPTER XIII. 

Boiler Design 468 

APPENDIX 503 

INDEX 529 



STEAM-BOILERS. 



CHAPTER I. 

TYPES OF BOILERS. 

Steam-boilers may be classified according to theTr form 
and construction or according to their use. Thus we have 
horizontal and vertical boilers, internally and externally fired 
boilers, shell-boilers and sectional boilers, fire-tube and water- 
tube boilers: the several features mentioned may be combined 
in various ways so as to give rise to a large number of kinds 
and forms of boilers. Again, we have stationary, locomotive, 
and marine boilers, together with a variety of portable and 
semi-portable boilers. Locomotive boilers are always shell- 
boilers, internally fired, and with fire-tubes ; and the re- 
strictions of the service have developed a form that has 
changed little from the beginning, except in the direction of 
increased size and power. Marine boilers present a much 
larger variety of form and construction, depending on the 
steam-pressure used and the size and service of the vessel to 
which they are supplied. The Scotch or drum boiler is more 
widely used than any other form at present, but the tendency 
to use high-pressure steam has led to the introduction of vari- 
ous forms of water-tube boilers for marine work. The variety 
of forms and methods of construction of stationary boilers is 
very wide : each country and section of a country is likely to 
have its own favorite type. Thus in New England, where 



2 S TEA M-B OILERS. 

the water is good, cylindrical tubular boilers are largely used; 
in some of the Western States, where water contains mineral 
impurities, flue-boilers are preferred; and in England, the 
Lancashire and Galloway boilers are favored; and again, 
various forms of sectional and water-tube boilers are now 
widely used. 

Cylindrical Tubular Boiler. — This type of boiler is shown 
by Figs, i and 2 and by Plate I. It consists essentially of a cylin- 
drical shell closed at the ends by two flat tube-plates, and of 
numerous fire-tubes, commonly having a diameter of three or 
four inches. About two thirds of the volume of the boiler is 
filled with water, the other third being reserved for steam. 
The water-line is six or eight inches above the top row of 
tubes. The tube-plates below the water-line are sufficiently 
stayed by the tubes ; above the water-line the flat plates are 
stayed by tJirougJi rods or stays as in Plate I, by diagonal 
stays like those shown by Fig. 91, page 229 or otherwise. A 
pair of cylindrical boilers in brick setting are shown by Figs. 
44 and 45, on pages 130 and 131, with the furnaces under 
the front (right-hand) end. The products of combustion pass 
back over a bridge-zvall, limiting the furnace, to the back end, 
then forward through the tubes and up the uptake to the flue 
which leads to the chimney. 

The shell commonly extends beyond the front tube-plate, 
as shown at the right in Fig. 1, and is cut away to facilitate 
the arrangement of the uptake. The boiler is usually sup- 
ported by cast-iron brackets riveted to the shell ; the front 
brackets may rest on or be fixed to the supporting side walls, 
but the rear brackets should be given some freedom to avoid 
unduly straining the boiler by expansion. Thus the rear 
brackets may rest on rollers, which in turn bear on a horizontal 
iron plate. The expansion takes place toward the back end of 
the boiler, and to allow for this expansion a space is left 
between the back tube-sheet, and the arch of fire-brick back 
of the boiler. 



TYPES OF BOILERS. 




STEAM-BOILERS. 




TYPES OF BOILERS. 5 

The boilers shown by Figs. 1 and 2 and by Plate I each have 
two steam-nozzles, one near each end. The safety-valve is 
usually attached to the front nozzle, which is above the fur- 
nace. The steam-pipe leading steam from the boiler is at- 
tached to the rear nozzle, which is over the back end of the 
boiler, where ebullition is less violent, and consequently there 
is less danger that water will be thrown into the steam-pipe. 

Boilers of this type commonly have a manhole on top near 
the middle, and a hand-hole near the bottom of each tube- 
sheet, as shown on Plate I, to give access to the interior of 
the boiler and to facilitate washing out. Many boilers are 
now made with a manhole near the bottom of the front tube- 
sheet, in addition to the one on top. All parts of the boiler 
can then be cleaned and inspected whenever desirable. Some 
of the lower tubes must be left out when there is a manhole 
in the tube-sheet, but this is of small consequence, as the 
lower tubes are not efficient, and enough heating-surface can 
be provided elsewhere. The omission of the lower tubes re- 
quires also special stays for the portion of the tube-sheet left 
unsupported. 

The feed-pipe for the boiler shown by Plate I enters the 
front head at the left, below the water-line, and runs toward 
the back end of the boiler, where it may end in a perforated 
pipe leading across the boiler. The feed-pipe may enter the 
top of the boiler, near the back end, and terminate in a similar 
perforated transverse pipe below the water-line. 

A blow-off pipe leads from the bottom of the shell near the 
back tube-sheet. On the blow-off pipe there is a plug or valve 
which may be opened when steam is up, to blow out mud and 
soft scale that may collect in the boiler. The boiler is com- 
monly set with a slight inclination toward the rear so that 
mud may collect near the blow-off pipe. The boiler may be 
emptied by allowing the water to run out at the blow-off pipe. 

About half of the shell, two thirds of the back tube-sheet, 
and all the inside surface of the tubes come in contact with 



6 STEAM-BOILERS. 

the products of combustion and form the heating-surface ; all 
the heating-surface is below the water-line. 

The boiler-setting, shown by Figs. 44 and 45 on pages 
130 and 131 is made of brick laid in cement or mortar; all 
parts that are directly exposed to the fire are lined with fire- 
brick. The walls have confined air-spaces to reduce transmis- 
sion of heat. The boiler front is commonly made of cast iron, 
and has fire-doors leading to the furnace, and ash-pit doors 
opening from the ash-pit, or space below the grate ; there are 
also large doors giving access to the tubes through the 
smoke-box at the front end of the boiler. The furnace is 
formed by the side walls, the bridge, and the lower part of the 
boiler front, which latter is lined with fire-brick above the 
grate. Doors through the rear wall give access to the space 
back of the bridge. The top of the boiler is covered by a 
brick arch or by non-conducting material. 

Two-flue Boiler. — The cylindrical flue-boiler differs from 
the tubular boiler mainly in replacing the fire-tubes by one 
or more large flues. Fig. 3 shows such a boiler with two 




Fig. 3. 



flues. This type of boiler is usually longer than a tubular 
boiler, but even so it has less heating-surface and is less 
efficient in the use of coal. Nevertheless the greater sim- 
plicity and accessibility for cleaning recommend it where feed 
water is bad. 

The setting of a flue-boiler resembles that for the cylin- 



TYPES OF BOILERS. 



drical tubular-boiler. 




The figure shows two loops at the top 
of the shell for hanging the 
boiler; a crude method of sup- 
porting, suitable only for small 
and short boilers. 

Plain Cylindrical Boiler. — 
In places where fuel is very 
cheap, especially where it is a 
waste product, as at sawmills, 
the plain cylindrical boiler is fre- 
quently used. Its external ap- 
pearance is similar to that of the 
two-flue boiler (Fig. 3), except 
that there are no flues and the 
ends are commonly hemispheri- 
cal or else curved to a radius 
equal to the diameter of the 
"* shell. Such plain cylindrical 
2 boilers are also employed to util- 
ize the waste gases from blast- 
furnaces. They are commonly 
30 to 42 inches in diameter and 
from 20 to 40 feet long. They 
have been made 70 feet long. 
With such extreme lengths spe- 
cial care must be taken to insure 
equal distribution of the weight 
to the supports and to provide 
for expansion. 

Lancashire Boiler. — This 
boiler, shown by Fig. 4, is a two- 
flue shell-boiler with furnaces 
in the tubes; it is therefore an 
p internally-fired boiler, in which 
it differs from the two pre- 



8 STEAM-BOILERS. 

ceding types, which are externally-fired. The chief difficulty 
in the design of these boilers is to provide sufficiently large 
furnaces without making the external shell too large. As com- 
pared with the cylindrical tubular boiler, this boiler will be 
sure to have long, narrow grates, with a shallow ash-pit and a 
low furnace-crown : the boiler also appears to be deficient in 
heating-surface. In compensation, radiation and loss of heat 
from the furnace are almost entirely done away with, and the 
thick outside shell, with its riveted joints, is not exposed to 
the fire, as with the tubular boiler. The flues are made in 
short sections riveted together at the ends, thus forming a 
series of stiffening rings that add very much to the strength 
of the flues against collapsing. Conical through-tubes, ver- 
tical or inclined, give increased heating-surface, break up the 
currents of the hot gases, improve the circulation of the water, 
and strengthen the flues. These tubes are small enough at 
the lower end to pass through the hole cut in the flue for the 
upper end, and thus are readily put in or taken out for repairs. 

The flat plates at the ends of the shell are stayed by 
gusset-stays or triangular flat plates to the shell of the boiler. 
The boiler is provided with a manhole near the back end and 
a safety-valve near the front end. Steam is taken through a 
horizontal dry-pipe, perforated on the top. 

Galloway Boiler. — This boiler has two furnace-flues at the 
front end, like the Lancashire boiler. Beyond the furnace 
the two flues merge into one broad flue, having the upper and 
lower surfaces stayed by numerous conical through-tubes, like 
those shown in Fig. 4 for the Lancashire boiler. 

Cornish Boiler. — This boiler was developed in conjunction 
with the Cornish engine, and both boiler and engine long had 
a reputation for high efficiency. It differed from the Lanca- 
shire boiler in that it had but one flue; it formerly did not 
have cross-tubes. The one furnace of the Cornish boiler, with 
a given diameter of shell, can have better proportions than 
the two furnaces of the Lancashire boiler, but there is even 



TYPES OF BOILERS. q 

greater difficulty to get sufficient grate-area and heating-sur- 
face- The high economy shown by these boilers when used 
with the Cornish pumping-engine was due to a slow rate of 
combustion, and to the skill and care of the attendant, who 
was usually both engineer and fireman, and who was stimu- 
lated by a system of competition and awards, maintained by 
the mine-owners in that district. 

The Lancashire and the Cornish boilers are set in brickwork 
which forms flues leading around the outside shell, thus mak- 
ing the shell act as heating-surface. Fig. 5 gives a cross-sec- 




Fig. 5. 



tion of the Lancashire boiler and its setting. After the gases 
from the fires leave the internal flues they are directed into 
the flue a and come forward ; then they are transferred to the 
flue b and pass backward ; finally they come forward in the 
flue c, and are then allowed to pass to the chimney. This 
forms what is known as a wheel-draught. In some cases the 
gases divide at the rear and come forward through both side 



TO STEAM-BOILERS. 

flues a and b> and uniting pass back through c and thence to 
the chimney, forming a split -draught. 

Vertical Boilers.— Boilers of this type have a cylindrical 
shell with a fire-box in the lower end, and with fire-tubes run- 
ning from the furnace to the top of the boiler. Large verti- 
cal boilers have a masonry foundation and a brick ash-pit; 
small vertical boilers have a cast-iron ash-pit that serves as 
foundation. Vertical boilers require little floor-space; if 
properly designed they give good economy, or they may be 
made light and powerful for their size, when economy is not 
important. 

Fig. 6 shows a large vertical boiler designed by Mr. 
Manning. It is made 20 to 30 feet high, so that there is a 
large heating-surface in the tubes. The shell is enlarged at 
the fire-box co provide a larger furnace and more area on the 
grate. The internal shell which forms the fire-box is joined 
to the external shell by a welded iron ring called the founda- 
tion-ring. This internal shell should be made of moderate 
thickness to avoid burning or wasting away under the action 
of the fire. Being under external pressure, the shell of the 
fire-box must be stayed to avoid collapsing. For this pur- 
pose it is tied to the outside shell at intervals of four or five 
inches each way, by bolts that are screwed through both 
shells and riveted over cold, on both ends. The stays near 
the bottom have each a hole drilled from the outside nearly 
through to the inside end. Should any stay break or become 
cracked, steam will escape and give warning to the fireman. 

The tubes are arranged in concentric circles, leaving a 
space about ten inches in diameter at the middle of the 
crown-sheet ; the corresponding space in the upper tube- 
sheet provides for the attachment of the nozzle for the steam 
outlet. 

There are numerous hand-holes in the shell outside of the 
fire-box, some near the crown-sheet, and some near the foun- 
dation-ring, and these are the only provision for cleaning the 



TYPES OF BOILERS. 



II 



WATER L.EVEL 




'&m& 



Fig. 6. 



12 



STEAM-BOILERS. 



boiler, which consequently is adapted for the use of good 
feed-water only. The feed-pipe enters the shell at one side 
and extends across the boiler; it is perforated to distribute 
the feed-water. 

The sides of the fire-box, the remaining surface of the 
tube-sheet allowing for the holes for the tubes, and the inside 




of the tubes up to the water-line form the heating-surface: 
the inside of the tubes above the water-line form the super 



TYPES OF BOILERS. 



13 



heating- stir face, since it transmits heat from the gases to the 
steam and superheats it. 

This type of boiler has found favor at factories where 
floor-space is valuable, since a powerful battery of boilers may 
be placed in a small fire-room. 

A small vertical boiler adapted for hoisting, pile-driving, 
and other light work is shown by Fig. 7. It commonly has 
a short smoke-pipe, into which the exhaust steam from the 
engine is turned to form a forced draught and give rapid 
combustion. Under this treatment the upper ends of the 
tubes frequently give trouble by leaking. To avoid this diffi- 
culty the tubes are sometimes ended in a sunken or submerged 
tube-sheet which is kept below the water-line, as shown by 
Fig. 8. The space between the edge of the tube-sheet 




Fig. 8. 



and the outside shell is likely to be contracted, and not to 
give proper exit for the steam formed on the tubes and 
crown-sheet. Furthermore, the cone forming the smoke- 
chamber above the tube-sheet is subjected to external pres- 
sure and is likely to be weak. 

A form of vertical boiler having a sunken tube-plate is 
shown by Fig. 9. It was at one time much used for steam 
fire-engines, but to save weight it was so crowded with tubes 



14 



STEAM-BOILERS. 



and the water-spaces were so contracted that it gave much 
trouble when forced. 

Fire-engine Boiler. — A boiler for a steam fire-engine 
should be light and compact, able to make steam quickly and 



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ooo ooce po o o o 




__k 

o o ooooo fr Jr 




Fig. 9. 

to steam freely when urged. They have small water-space 
and large heating-surface for their size, but are not economi- 
cal in the use of fuel. It is customary to use cannel-coal for 
fire-engines, as it. burns freely without clogging. A forced 



TYPES OF BOILERS. 



15 



draught is obtained by exhausting steam up the smoke-pipe. 
When standing in the engine-house ready for duty the 
boilers are kept hot by connecting them to a heating- 
boiler in the basement. The connection is so made with 
snap-valves that it is broken by pulling the fire-engine out of 
position. 




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Fig. 10. 



Scotch Boilers. — A single-ended three-furnace Scotch 
marine boiler is shown in perspective by Fig. 10; Fig. it 
gives the working drawings of a similar boiler with two fur- 
naces. The arrangement of the furnaces in the flues, is simi- 
lar to that for the Lancashire boiler, shown, by Fig. 4. The 
furnace-flue leads into a combustion-chamber, from which 



1 6 STEAM-BOILERS. 

the products of combustion pass through fire-tubes to the 
uptake, which is bolted onto the front end of the boiler. 

The flues are from three and a half to four and a half 
feet in diameter; the size of the boiler depends on the 
number and size of the flues. Large boilers have as many 
as four flues. A three-furnace boiler commonly has three 
combustion-chambers, while a four-furnace boiler may have 
two, into each one of which two furnaces lead. Double- 
ended boilers have furnaces at each end, and resemble 
two single-ended boilers placed back to back. A double- 
ended boiler is lighter, cheaper, and occupies less space than 
two single-ended boilers. In the best practice there are 
two distinct sets of combustion-chambers for the two sets 
of furnaces. To still further lighten double-ended boilers, 
common combustion-chambers for corresponding furnaces at 
the two ends have been used. The results from such 
boilers have not been satisfactory, more especially when 
used under forced draught in the closed stoke-holes of war- 
ships; there has been so much trouble from leaky tubes 
under such conditions that forced draught has been aban- 
doned in many cases, and ships have consequently failed to 
make the speed anticipated. 

The circulation of water is defective in all Scotch boilers, 
and more especially in double-ended boilers. Considerable 
time — three or four hours — is always allowed for raising steam. 
Frequently some arrangement is made for drawing cold water 
from the bottom of the boiler and returning it near the water- 
line, while steam is raised. Haste and lack of care are liable 
to cause leakage from unequal expansion. The flue has the 
highest temperature of any part of the boiler and consequently 
expands the most, so that some allowance for expansion must 
be made or it will strain the tube-sheets and cause leaks. The 
methods of providing for expansion and at the same time 
stiffening the flues against collapsing under external pressure 
are shown on pages 291 to 3 it, and will be described in de- 
tail later on. 



TYPES OF BOILERS. 



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i8 



STEAM-BOILERS. 



Locomotive-boilers. — The typical American locomotive- 
boiler is shown by Plate II. Fig. 12 gives a perspective view 
of a boiler of the locomotive type used for small factories, or 
where steam is required temporarily ; it has no permanent 
foundation, but is supported on brackets at the fire-box and 
by a pedestal-bearing on rollers near the back end. 

The locomotive-boiler consists essentially of a rectangular 
fire-box and a cylindrical barrel through which numerous tubes 
pass from the fire-box to the smoke-box, which forms a con- 
tinuation of the barrel, and from which the products of com- 
bustion pass up the smoke-stack. 

The fire-box is joined to the outer shell at the bottom by 
a forged rectangular foundation-ring, similar (except in shape) 




Fig. 12. 



to the foundation-ring of a vertical boiler. Near this ring are 
several hand-holes for clearing out the space between the fire- 
box and the shell, commonly called the water-leg. The boiler 



TYPES OF BOILERS. 



19 



also has a manhole at the top of the barrel. The water-leg is 
stayed by screwed stay-bolts riveted cold at the ends. 

The flat crown-sheet is stayed to a system of crown-bars 
which rest on the side sheets of the fire-box and are also slung 
from the shell. 

Plate III shows a locomotive-boiler with a flattened top over 
the fire-box to which the crown-sheet is stayed by through-bolts. 

The excessive compression brought to the sheets, forming 
the inner sides of the water-leg, by the crown-bars which get 
an end support at these sheets and the great depth required in the 
crown-bar in order to give the strength needed, have made it 
impracticable to use crown-bars on boilers carrying more than 
200 lbs. of steam-pressure. 

The method shown by Plate III is commonly adopted on 
large boilers of this class. The stay-bolt has a tapering head 
which is drawn into a tapering hole in the crown-sheet. This 
makes a tight joint and does not increase to any extent the amount 
of metal in contact with the crown-sheet. 

The whole matter of staying will be discussed more fully in 
the chapter on staying. 

The tubes for a locomotive-boiler are smaller than for a sta- 
tionary boiler and are spaced much more closely. Generally 
about 2 -inch tubes are used in locomotives, although in some 
cases smaller tubes have been used. The tubes are spaced at 
the intersection of sets of parallel lines drawn at angles of 30 and 
150 with reference to a horizontal line. 

By this means a greater number of tubes can be gotten into 
a given space than could be done by spacing in vertical and 
horizontal rows, as is customary in horizontal multitubular boilers 
like Figs. 1 and 2 and Plate I. This is to obtain a large heating- 
surface required by the high rate of combustion, which often 
exceeds one hundred pounds of coal per square foot of grate- 
surface per hour. The boiler works under a strong forced 
draught, produced by throwing the exhaust up the smoke-stack. 

The boiler is fastened rigidly to the frame of the locomo- 



20 STEAM-BOILERS. 

tive at the smoke-box end; a small longitudinal motion on the 
frame at the fire-box end is provided by expansion-pads, shown 
by Fig. 4, Plate II. 

Locomotive Type of Boiler.— Reference has already been 
made in connection with Fig. 12 to a boiler of locomotive type 
used for stationary purposes. Plate IV shows a modification 
of the locomotive type designed by Mr. E. D. Leavitt to give 
high evaporative efficiency. The boiler represented has a barrel 
90 inches in diameter, and it is 34 feet 4 inches long over all. 
The working pressure is 185 pounds. 

The fire-box of this boiler is spread at the bottom to give 
increased grate-area, and contains two separate furnaces, shown 
by the section A A on Plate IV. The products of combus- 
tion pass through openings, shown by section BB, into a com- 
bustion-chamber, which has the section shown at CC. From 
the combustion-chamber, the gases pass through tubes to the 
smoke-box and uptake. As far as the combustion-chamber 
the top of the boiler is flattened to facilitate the staying of the 
crown-sheets of the furnace, passages, and combustion-cham- 
ber; the barrel of the boiler beyond the combustion-chamber 
is cylindrical. 

The boiler is somewhat complicated in construction and 
staying, and must be handled with care, especially in starting, 
to avoid straining from unequal expansion. It is adapted for 
the use of good feed-water only. 

Boilers of the locomotive type were at one time used for 
torpedo-boats. The fire-box was made shallower than for 
locomotive-boilers, and forced draught in a closed stoke-hole 
was used, the rate of combustion being even higher than on 
locomotives. Whatever may have been the reasons, it was a 
fact that this type of boiler, which is very reliable on locomo- 
tives, gave much trouble in torpedo-boats. 

Water-Tube Boilers. — The boilers thus far considered 
have an external shell containing a large body of water. Heat 
is communicated to the water through the shells or through 



TYPES OF BOILERS. 21 

the sides of internal furnaces, and also by carrying the gases 
through tubes or flues. The boilers and water contained, are 
heavy and cumbersome, and the shells under high pressure 
must be made very thick. If the boiler fails either through 
some defect or through carelessness of attendants, a disastrous 
explosion is likely to take place. If properly designed and 
made and if cared for by competent and careful attendants 
they are safe, reliable, and durable. The large mass of hot 
water tends to keep a steady pressure, though at the expense 
of rapidity of raising steam or of meeting a sudden demand 
for more steam. 

A large number of water-tube boilers of all sorts of shapes 
and methods of construction has been devised to overcome 
the admitted defects of shell-boilers. They all have the 
larger part of their heating-surface made up of tubes of moder- 
ate size filled with water. They all have some form of separa- 
tors, drum, or reservoir in which the steam is separated from 
the water; some of these boilers have a shell of consider- 
able size, thus securing a store of hot water and a good free- 
water surface for disengagement of steam. Such shell, drum, 
or reservoir is either kept away from the fire or is reached 
only by gases that have already passed over the surface of 
water-tubes. 

The tubes are of moderate or small diameter, and so can 
be abundantly strong even when made of thin metal. Even 
if a tube fails through defect in manufacture or through wast- 
ing during service, it will not cause a true explosion ; and yet 
the failure of a tube in a confined boiler or fire-room has fre- 
quently caused death by scalding. 

Water-tube boilers may be made light, powerful, and 
compact, and are well adapted for use with forced draught. 
Steam may be raised rapidly from cold water, but pressure 
falls as rapidly if the fire loses intensity, and fluctuations in 
pressure are likely to occur. The two greatest difficulties are 
to secure a proper circulation of water through the tubes 



22 STEAM-BOILERS. 

and to properly separate the steam from the water. There 
are many joints that may give trouble by leaking, and some 
types have numerous hand-holes for cleaning the tubes, which 
may further increase the chances of petty leaks. 

A few water-tube boilers will be described as illustrations ; 
many others equally good will be passed by, since it will be 
impossible to describe all. 

Babcock and Wilcox Boiler.— This boiler, which is 
shown by Figs. 13 and 14, is a water-tube boiler having one or 
two cylindrical drums at the top from either end of which are 
suspended " headers" into which the tubes running from end 
to end are expanded. 

The headers are made of steel castings or forgings, box-like 
in shape, with holes for tubes staggered so that the tubes taken 
as a whole are in horizontal rows, but not in vertical rows — an 
arrangement that gives a better spreading of the products of 
combustion among the tubes. 

Opposite the end of each tube there is a hand-hole, as shown. 
Each header is connected with the corresponding header at the 
opposite end by the tubes making a "section." The capacity of 
a boiler of this class is increased by increasing the number of 
tubes in a section and by increasing the number of sections con- 
nected to the drum or drums at the top: thus a boiler 12 wide 
and 9 high would have 12 sections and 9 tubes in each header. 
If there were a very strong draught it might be advisable to have 
more tubes in a header. 

A double-deck boiler is one where a second header is joined 
to the end of the first header. The two headers are joined by 
a piece of tube which is expanded into each. Two headers, 
each 9 high, when joined in this way make 18 high. 

By means of a special tile made to fit between the tubes the 
gases are obliged to circulate, as shown by the arrows. 

The gases escape out of the back wall. In some cases where 
there is not much room the gases have been brought up between 
the drums at the back end, thus enabling the back wall to be 



TYPES OF BOILERS. 23 

MMMliUUMMUUUUMHdlWlMMIIUl 




24 STEAM-BOILERS. 

against the wall of the building. The lower half of the cylin- 
drical shell serves as heating-surface, but it is at such a height 
above the fire and is so shielded by the water-tubes that it is not 
liable to be overheated. The boiler is hung from cross-girders 
front and back, which in turn are supported on iron columns, 
and the brick setting is only a screen to retain the heat. 

The circulation of the water in the boiler is down from the 
shell at the rear to the water-tubes, forward and upward through 
the tubes, in which course it is partially vaporized and conse- 
quently has a less average density, then up into the shell at 
the front, where the steam and water separate; the water in the 
shell flows continually from the front to the rear to supply the 
current through the tubes. 

Beneath the back headers there is a mud-drum into which 
scale settles. The blow-off pipe leads from this mud-drum out 
through the setting. 

Heine Boiler. — This boiler, shown by Fig. 15, consists of 
one or two drums, depending on the size of the boiler, with a rec- 
tangular box-like water-leg connected at each end. 

These legs are built out of plate and riveted to the drum or 
drums. 

Tubes run from leg to leg. Opposite the end of each tube 
there is a hand-hole through which the tube may be expanded 
or cleaned from scale. The boiler is set with the back end com 
siderably lower than the front end, as shown by the cut. 

The gases are made to circulate, as indicated by the arrows. 

The feed-water is taken into a small drum inside the main 
drum. It becomes heated here and deposits some of the lime 
salts, which are generally found in feed-water. These deposits 
are blown out from time to time through the pipe shown. A 
similar blow-off connection is shown at the bottom of the back 
water-leg. 

The water circulation is from the front towards the back in 
the drum and from the back towards the front in the tubes. 

A mixture of steam and water rushes out of the tubes at the 



TYPES OF BOILERS. 



25 



front end and up into the drum where it strikes against a deflect- 
ing plate placed so as to keep water from being sprayed into the 
steam space. 

A similar plate is to be found in the drum of the Babcock 
and Wilcox boiler. The velocity into the drum is greater in the 
Babcock and Wilcox than in the Heine. 

The water-legs of the Heine boiler are stayed by hollow stays 




^fjif^^^^ 



pis 



Fig. 15. 
expanded or screwed into the two plates at points located between 

the tubes. 

The Stirling Boiler. — This boiler, shown by Fig. 16, has 
three cylindrical drums at the top and a larger drum at the 
bottom, connected by tubes having a slight curvature at the 
ends. The two forward drums at the top have also a connec- 
tion below the water-line through pipes not indicated. All 
three upper drums have their steam-spaces connected by 
piping. The water-line is indicated by a dotted line. 



26 



STEAM-BOILERS. 



The feed-water is introduced into the rear upper drum, 
from which it passes down through the rear system of pipes, 
which act mainly as a feed-water heater, and enter the lower 
drum, where the water deposits any lime compound that it 
may contain, from whence it may be blown out at intervals. 
Fire-brick bridges cause the products of combustion to pass 
in succession through the three systems of water-tubes as 
shown by the arrows. 




Fig. 16. 



The circulation through the tubes is very rapid and the tubes 
being nearly vertical do not collect much scale. 

These two facts have made this boiler work satisfactorily 



TYPES OF BOILERS. 



2 7 



with bad feed-water when some other types of boiler would not 
answer at all. 

The water-level is not the same in all three drums when the 
boiler is working. The front drum will show a level 6 inches 
higher than the rear drum if the boiler is forced hard. 

Water Tube Marine Boilers. — With the advent of very 
high steam pressures on steamships there has been a tendency 
to replace the Scotch boiler by some form of water-tube boiler. 

The objects that are sought in water-tube boilers for steam- 
ships are a larger power for the weight and the ability to carry 
high pressures. 

It is still a question whether the water-tube boiler will or 
can replace the Scotch boiler. 




Fig. 17. 

Babcock and Wilcox Marine Type.— This boiler, shown 
by Fig. 17, is made up of sections connected at one end to the 



2 8 STEAM-BOILERS. 

bottom of a drum running at right angles to the tubes, and at the 
other end to a tube leading into the side of the drum at the level 
of the water-line. The side sections are continued down to the 
level of the grate, the tubes being replaced by forged steel boxes 
of 6-inch square sections at the furnace sides. These boxes are 
located one above the other on the same angle as the tubes; they 
take the place of brickwork, insure a cool side casing, and prevent 
the adherence of clinkers. 

Placed across the bottoms of the front header ends and con- 
nected with them by 4-inch tubes is a forged steel box of 6-inch 
square section. 

This box is situated at the lowest corner of the bank of tubes 
and forms a blow-off connection or mud-drum, through which 
the boiler may be completely drained. 

The circulation of water in the tubes is from the front to the 
back, w"here the connecting-tube leading from each section to 
the drum discharges a mixture of steam and water against the 
baffle in the large drum. 

The path of the gases is shown by the arrows. 

The Belleville Boiler is represented by Fig. 18; it con- 
sists essentially of a series of coils of pipe made up with bends 
and elbows around which the products of combustion pass 
on the way to the chimney. At the top there is a steam-drum 
Ay connected by two circulating-pipes B and C, with a drum 
D at the bottom. From the mud-drum D a rectangular feed- 
supply runs across the front of the boiler to all the coils or 
elements of the boiler. Each element is continuous from the 
feed-supply to the steam-drum, and is made up of slightly 
inclined pieces of pipe with horizontal bends or connections 
at the end. The effect is much as though a helical coil were 
flattened into two vertical tiers of pipes. The amount of 
water in the boiler is so small that it cannot be run without 
an automatic feed-water regulator, which in turn requires the 
attention of an expert feed-water tender. The several ele- 
ments deliver a mixture of water and steam to the steam- 



TYPES OF BOILERS. 



29 



r-^fl^5 




■& 



2)\PlPlPlPl&lPlp^\ 



o 



o 






- 







i 

«: > 

i 

i 

1 I 



El 



H 



B 



^ 




30 STEAM-BOILERS. 

drum, which does not appear to act efficiently as a separator, 
as an external separator is placed between the boiler and the 
engine. The feed-water is supplied to the steam-drum and 
passes through the external circulating-pipes to the mud-drum, 
where it deposits much of its impurities. 

Thornycroft Boiler. — The boiler represented by Figs. 19 
and 20 was built for the torpedo-boat destroyer, "Daring," 
by Mr. Thornycroft; boilers of slightly different forms have 
been fitted by him, in torpedo-boats and steam-launches. 

The boiler consists essentially of a large drum or separator 
at the top and three drums at the bottom, connected by a large 
number of bent-tubes. There is, inside of the casing, a large 
tube connecting the top drum to the middle drum at the bottom, 
and this drum is connected to the side drums by smaller pipes. 
The circulation is down from the top drum to the middle lower 
drum, and from that to the side drums, then up through all the 
bent water-tubes to the upper drum, where mingled water and 
steam is delivered against a baffle-plate above the water-line. 
Steam is drawn from a nozzle at the front end of the top 
drum. 

The arrangement of grates and fire-doors is shown in 
elevation and section by Fig. 19. The middle drum divides 
the grate into two parts; over that drum is a space which is 
in communication with the uptake, as shown by Fig. 20. 
The products of combustion pass among the tubes leading 
from the middle drum; the tubes to the outer drums intercept 
the radiant heat which would otherwise strike on the boiler- 
casing. 

The boiler-setting is an iron frame, and the casing is thin 
plate iron lined with incombustible non-conducting material. 
There are numerous doors through the casing for cleaning the 
tubes. 

This boiler has proved very successful with a forced 
draught, making steam freely and giving little trouble. The 
boiler contains so small an amount of water that steam may 



TYPES OF BOILERS. 



31 





3 2 



STEAM-BOILERS. 



be raised quickly, and any demand for steam can be quickly 
met. On the other hand, the feed-supply must be regulated 
with care and skill, and the pressure is liable to fluctuate. 




Fig. 21. 



The Yarrow Boiler. — The form of boiler used by Mr. 
Yarrow for torpedo-boats, is shown by Fig. 21. It resem- 
bles in general arrangement a form used by Mr. Thorny- 



TYPES OF BOILERS 33 

croft with one grate. It, however, differs radically in certain 
particulars, namely, in that the tubes are straight and that 
they enter the upper drum below the water-line, and in that 
there are no pipes outside the casing to carry water from the 
upper drum to the lower drum or reservoirs. Some of the 
tubes deliver water and steam to the upper drum, from which 
steam is drawn ; other tubes carry water from the upper 
drum to the lower drums. A given tube may act sometimes 
in one way and sometimes in the other. Naturally those 
tubes which receive the most heat and make the most steam 
deliver to the upper drum, and tubes that receive less heat 
carry down water. 

The air for the fire is drawn from an iron box or casing 
outside the boiler-casing, so that the heat escaping from the 
boiler-casing is largely carried back to the fire, and the fire- 
room, and also the rest of the vessel, is heated up less. 

The Almy Boiler. — This boiler, which is represented by 
Fig. 22, is made of short lengths of pipe screwed into return- 
bends and into twin unions. At the bottom is a large tube or 
pipe forming three sides of a square at the sides and back of 
the grate. From this water-space the tubes lead into a similar 
structure at the top. The steam and water are discharged into 
a separator in front of the boiler, from which steam is drawn; 
while the water separated therefrom, together with the feed- 
water, passes down through circulating-pipes to the bottom of 
the boiler. 

The boiler is provided with a coil feed-water heater above 
the main boiler. It is enclosed by a casing lined with non- 
conducting material. It is intended for general marine work. 

General Discussion. — In deciding on the type of boiler to 
be selected for any particular case there are a number of things 
to be considered. The following are the most important: 

1. The pressure to be carried. 

2. The quality of the feed-water. 



34 



STEAM-BOILERS, 



3. The variation in load. 

4. The size of the battery. 

5. The amount of land available. 

6. The cost of land. 

7. The fuel to be used. 

In general, it may be said that the more simple the boiler Is, 
the better it is; that all parts of the boiler should be easily 




Fig. 22. 



accessible, and that the boiler should be so designed that it will 
not strain itself by unequal expansion. 

The thickness of the steel needed in the shell of a boiler must 
increase as the pressure increases, and also as the diameter 
increases, as will be shown later. It is not considered advisable 



TYPES OF BOILERS. 35 

to transmit heat through plates over one half an inch in thick- 
ness. 

For high pressures this means that if shell boilers, like Figs. 1 
and 2, are to be used the diameter must not be greater than 
60 or 66 inches, thus limiting the horse-power of a single unit 
to from 80 to 125 boiler horse-power, depending on the kind of 
coal used and the rate of combustion. 

This type of boiler is the least expensive, and if there were 
ample room and if the land occupied were inexpensive, it might 
be advisable to instal a large number of these small units to 
make up the horse-power desired. If, however, land were ex- 
pensive, or if there were but a small amount of land available, 
then this type could not be considered. 

A vertical boiler, like the Manning, or some form of water- 
tube boiler, like the Babcock and Wilcox, the Heine, or the 
Stirling, would probably be selected. 

If the cost of land were extremely high water-tube boilers 
might be located on the second, third, and fourth floors of a build- 
ing and discharge steam into a common main supplying engines 
in the basement. This arrangement is common in power- and 
lighting-stations located in the middle of a city. 

There is no difficulty in making a building sufficiently strong 
to carry the weights. 

There should be a sufficient number of boilers in the battery, 
so that one could be shut down and the others carry the load. 
As a boiler can be run from 25 to 30 per cent over its rated 
capacity this means that there should be at least four boilers 
in the battery if the plant is to run continuously. It is not cus- 
tomary to install units of more than 350 or 500 horse-power even 
in the largest batteries. 

The quality of the feed-water must also be considered in 
deciding how many boilers there are to be in the battery. If 
the feed-water is very bad it may be necessary at times to have 
two boilers shut off from the line. More boilers are needed when 
the feed-water is of poor quality, not only for the reason mentioned, 



36 STEAM-BOILERS. 

but also because of the poorer efficiency of the heating-surface 
due to deposits of scale. 

The heating value of the fuel also enters as a factor in deter- 
mining the number of boilers needed. 

If a steady pressure is to be maintained with as little fluctua- 
tion as possible, a boiler with a large water-space should be 
chosen. Such a boiler will meet a sudden demand for steam 
without much drop in pressure; on the other hand, it takes a 
long time to increase the pressure. 

The Scotch boiler and a modification of the same having the 
combustion-chamber in a space bricked in at the end of the 
boiler have been used successfully for the operation of draw- 
bridges, where the demand for steam is at the rate of 100 boiler 
horse-power for a period of from five to eight minutes two or 
three times an hour. 

The cost of boilers varies with the price of steel. At the 
present time, 1912, horizontal multitubular boilers cost, when 
set, about $11.50 per horse-power for boilers 60 to 66 inches in 
diameter. 

Water-tube boilers about 200 horse-power per unit cost from 
$15.50 to $16.50 per horse-power, set ready to connect to the 
steam-main. 

Scotch boilers cost about $16.50 per horse-power in sizes 
ranging from 100 to 150 horse-power. 

Tables giving the diameters, ratings, width, length, and 
heights of settings of many of the common types of boilers have 
been added to the appendix. 

We believe that these tables will be useful to any one who 
may be making the preliminary design of a boiler plant. 



CHAPTER II. 

SUPERHEATERS. 

Steam may be dry and saturated, primed or superheated. 

Dry and saturated steam and primed or "wet" steam, as it 
is sometimes called, at the same pressure have the same tem- 
perature. 

As bubbles of steam break through the surface of the water 
in a boiler some water is atomized into the steam-space where it 
floats just as moisture floats in the air. 

The amount by weight of such water floating in a total weight 
of one pound is called the priming. This priming is in certain 
types of boilers between .005 and .03. 

If heat is now added to the wet steam in the steam-space 
the water floating in the steam will vaporize and at the instant 
when all of this water has vaporized we have dry and saturated 
steam. If more heat is added the temperature of the steam will 
go up and the steam will become superheated; the amount of 
superheating in degrees being the difference between the tem- 
perature of the steam as observed and that of saturated steam 
of the same pressure. 

The specific heat of superheated steam is the amount of heat 
necessary to raise the temperature of one pound of superheated 
steam i° Fahrenheit. 

The specific heat has been found to increase with the pressure 
of the steam, and at any constant pressure to decrease as the 
number of degrees of superheating increases up to a certain point, 

37 



3* 



STEAM-BOILERS. 



differing somewhat for each pressure, beyond which the specific 
heat gradually increases. The degrees of superheat at which 
the values begin to increase are above any used in general engi- 
neering work. 

Specific Heat of Superheated Steam. — The following table 
gives the mean value of the specific heat of superheated 
steam for different degrees of superheat at a number of 
pressures. 

SPECIFIC HEAT OF SUPERHEATED STEAM. 



6 

< . 




!2 

'3 

D 1 




d 

.2 

1 



& 

03 
> 

"o 

w 


H 
O 

J 5 


Mean Value of the Specific Heat. 


Si" 


(Do 
+» ro 

*o£ 

4J O 

cd_Q 


Degrees of Superheat ° F. 


IJ 


10 


50 


IOO 


IS© 


200 


250 


300 


400 


500 


600 


IO 
3° 
50 
IOO 
I50 
200 
250 
300 


193.2 

250.3 
281.0 

327-9 
358.5 
381.9 
401 .1 

417-5 


l6l 
219 
25O 
298 
330 

354 
374 
39i 


3 

1 

4 
5 



3 
2 

3 


981.4 

944-4 
922 .8 
887.6 
863.0 

843-5 
826.9 
812.4 


1142.7 

1163.5 
1173.2 
1186.1 
1193.0 
1197.8 

1 201 . 1 

1203.7 


.46 
•49 
•5i 
•57 
.62 
.69 
• 77 
•85 


.46 
.48 
•5o 
•55 
•59 
•63 
.68 
.72 


.46 
.48 
• 50 

•53 
•56 
•59 
.62 
.64 




46 
48 
49 
52 

54 
56 
58 

(.0 




46 
48 
40 
5- 
53 
55 
56 
58 




46 
48 

40 
51 
52 
54 
55 
56 




46 
48 
49 

5i 
52 
53 

54 
55 




47 

48 
48 

50 
5i 
52 

53 

54 




47 
48 
48 

5o 
5i 
51 

52 
53 




47 
48 
48 

40 
50 
51 
52 
52 



The use of this table will be explained by applying the values 
to one or two simple problems. 

How many heat units must be added to a pound of feed- 
water at ioo° F. in order to change it into steam at 200 pounds 
absolute pressure, the steam being superheated 250 ? 

To change a pound of water at 32 into saturated steam re- 
quires 1 197.8 heat units. As the specific heat of water is practi- 
cally unity, the amount required to change the pound of water 
at ioo° into saturated steam would be 100 — 32 = 68 heat units 
less. Hence 1 197.8 — 68 + .54 X 250 = 1264.8. The value 
.54 is the specific heat taken from the table. 

The temperature of steam in a boiler is 545. 2 F., the 



SUPERHEA TERS. 3 9 

pressure is 175 pounds absolute, the feed- water is at 200 F. 
How many heat units are required to change a pound of feed- 
water into steam of this pressure and temperature? 

The temperature of saturated steam at 175 pounds may be 
found near enough for this illustration by assuming the tempera- 
ture between 150 and 200 pounds to vary uniformly with the 
pressure 

38I.9-358-5 x ^ = g + = o p 

5° 

as the temperature of saturated steam at 175 pounds. 
The superheat is 545.2 — 370.2 = 175 . 

a 8 
1193.0 + ^- X 25 - (200 - 32) + .545 X 175 = 1122.8. 
5° 

In a later chapter work of this sort is illustrated more fully. 

Attached Superheater. — There are two classes of super- 
heaters, the attached and the independently fired. 

The attached is connected to the boiler, receives its heat from 
the fire under the boiler, and in general does not give more than 
150 degrees of superheat. 

Nearly all of the attached superheaters are connected to the 
steam and to the water-space of the boiler in such a way that 
they can be flooded while steam is being gotten up in the boiler. 

Some makes of attached superheaters may be flooded and 
the heating-surface used as additional steam-generating surface 
when the boiler is delivering saturated steam. 

Babcock and Wilcox Attached Superheater.— This 
superheater is shown by Fig. 23. It is located directly under 
the drums between the first and second gas passages. It is made 
of bent tubes expanded into steel headers, as shown. 

Steam is taken from the dry pipe in the top of each drum 
into the center of the top headers, and after passing through the 
tubes leaves at the outer end of the bottom header. From the 



4Q 



STEAM-BOILERS. 



end of the bottom header a pipe leads up to a nozzle fastened to 
the drum of the boiler, but not connecting with the drum. In 
some instances these superheaters have been arranged to work 




Fig. 23. 



flooded with water when the boiler was not delivering superheated 
steam. 

Heine Attached Superheater. — Fig. 24 and the two 
cross-sections shown on the same cut gives the arrangement of 
the Heine superheater. 

The greater part of the products of combustion is made to 
circulate, as shown by the dotted arrows, and is utilized in generat- 
ing steam. 

A small part of the products of combustion is made to follow 
the path shown by the full arrows, and pass through the super- 
heater. The path of these gases will be made clear by the sec- 
tions BB and A A. 

Stirling Attached Superheater.— The attached super- 
heater is shown as the middle bank of small tubes in Fig. 25. 
The detail of this superheater is shown by Fig. 26, which is a 
cross-section taken through Fig. 25. 



SUPERHEATERS. 



41 





o ' 




42 



STEAM-BOILERS. 



Saturated steam from the front and rear drums enters the left- 
hand section of the upper drum (Fig. 26) through the holes shown 
near the top. This steam circulates through the tubes to and 




Fig. 25. 



from the lower drum, as shown by the arrows, and is drawn off 
at the right-hand end of the upper drum. 

There is a removable diaphragm in the lower drum and covers 
in the two diaphragms in the upper drum. These are provided 



SUPERHEATERS. 



43 



so as to make it possible for a man to get at the ends of any tubes 
which may need to be re-expanded. 

When using saturated steam the two by-pass valves in the 
diaphragms in the upper drum are opened and the lower drum 




Fig. 26. 

is connected with the bottom of one of the other drums through 
valves and piping provided for flooding. 

Independently -fired Superheater. — The independently- 
fired superheaters are intended to give higher temperatures to 
the steam than can be obtained by an attached superheater. 



44 



STEAM-BOILERS. 



Superheaters of this class give a thermal efficiency of about 
60 per cent. Different makers use different amounts of heating- 
surface for the same capacity and the same degrees of superheat- 
ing. It seems that about 3 square feet are needed per boiler 
horse-power if the steam is to leave at about 6oo° F. and was not 
primed more than one per cent on entrance to the superheater. 

In order to keep the temperature of the superheated steam as 
uniform as possible it is customary to make use of a Dutch oven 
furnace, a furnace with a fire-brick arch over the grate. This 
arch, by giving up heat at one time and by absorbing heat at 
another time, tends to keep the gases more nearly at a uniform 
temperature. 

Foster Independently- fired Superheater. — This is 
shown in longitudinal view by Fig. 27. Fig. 28 gives a section 




through a tube and header and shows the cast-iron rings put on 
to give additional surface for absorbing heat, and also to prevent 
any rapid fluctuations in the temperature of the fire affecting the 
temperature of the steam. 



SUPERHEATERS. 



45 



The inner tube shown in this cut is sometimes closed togethcx 
at the ends but not tightly sealed. This tube, which is held in 
place by distance pieces in the shape of rivet-heads, causes the 



AAAJXATr 




Fig. 28. 



steam to flow rapidly through the annular space between it and 
the outer tube. 

The steam enters Fig. 27 at the top and leaves at the bottom. 

American Independently-fired Superheater. — The 
American superheater is shown by Fig. 29. Like the preceding 
it is built with a Dutch oven-furnace. 

A " tempering" door located in the bridge-wall may also be 
used for regulating the temperature of the gases. 

The superheater is made up of headers, which are steel cast- 
ings joined together by steel tubes. The tubes from the bottom 
of one header enter the top of the header opposite. The steam 
circulates as many times as there are headers in one row and 
passes out at the bottom. 

The bottom tubes are of Shelby drawn nickel-steel and in 
some cases are covered with tile or cast iron. 

The headers are supported one on top of another with steel 
balls in between. These balls provide for the expansion sf the 
tubes. 



4 6 



STEAM-BOILERS. 




* 



SUPERHEATERS. 47 

A superheater of this make, installed at the Massachusetts 
Institute of Technology, designed to superheat 10,000 pounds 
of steam an hour at 250 pounds pressure with one per cent prim- 
ing, 250 F., had a grate-area of 15.6 square feet and 558.3 square 
feet of heating-surface. 

Steam Pipe-fittings for Superheated Steam. — Steel 
castings are probably the best fittings to use on pipe lines carry- 
ing highly superheated steam. Steel fittings are expensive and 
are not to be found in stock. 

There is evidence tending to show that cast iron, especially 
if of a poor grade, is affected in its strength by superheated steam: 
there is no evidence, however, showing that gun-iron fittings 
have deteriorated under the action of superheated steam. 

Fittings on superheated steam lines are subjected to greater 
strains on account of the larger amount of expansion of the 
pipe and on account of the greater changes in temperature. 

Composition loses its strength at high temperatures and is 
unsafe to use with superheated steam. 



CHAPTER III. 
FUELS AND COMBUSTION. 

THE fuels used for making steam are coal, coke, wood, 
charcoal, peat, mineral oil, and natural and artificial gas. 
Various waste and refuse products, such as straw, sawdust, 
and bagasse, are burned to make steam. 

All coals appear to be derived from vegetable origin, and 
they owe their differences to the varying conditions under 
which they were formed or to the geological changes which 
they have undergone. 

Anthracite Coal consists almost entirely of carbon and 
inorganic matters ; it contains little if any hydrocarbon. 
Some varieties, for example certain coals found in Rhode 
Island, appear to approach graphite in their characteristics, 
and are burned with difficulty unless mixed with other coals. 
Good anthracite is hard, compact, and lustrous, and gives a 
vitreous fracture when broken. It burns with very little 
flame unless it is moist, and gives a very intense fire, free 
from smoke. Even when carefully used, it is liable to break 
up under the influence of the high temperature of the furnace 
when freshly fired, and the fine pieces may be lost with the 
ash. 

Semi-anthracite or Semi-bituminous Coal is intermedi- 
ate in its properties between anthracite coal and bituminous 
coal; it contains some hydrocarbon, is less dense than anthra- 
cite, it breaks with a lamellar fracture, and it burns readily 
with a short flame. 
4 8 



FUELS AND COMBUSTION. 49 

Bituminous Coals contain a large and varying per cent 
of hydrocarbons or bituminous matter. Their physical prop- 
erties and behavior when burning, vary widely and with all 
intermediate gradations represented, so that classification is 
difficult. Three kinds may, however, be distinguished, as 
follows : 

Dry bituminous coals, which burn freely and with little 
smoke and without caking. 

Caking bituminous coals, which swell up, become pasty, 
and cake together in burning. They are advantageously used 
for gas-making. 

Long -flaming bituminous coals, which have a strong ten- 
dency to produce smoke ; some do and some do not cake 
while burning. 

Coke is made from bituminous and semi-bituminous coal 
by driving off the hydrocarbons by heat. Coke made as a 
by-product in gas retorts, is weak and friable, and has little 
value for making steam. Coke made in coking ovens, by 
partial combustion of the coal which is coked, is of a dark- 
gray color, porous, hard, and brittle. It has a metallic lustre, 
and gives out a slight ringing sound when struck. Sulphur 
in the coal may be burned out in coking, if the coal is moist 
or if steam is supplied during coking, so that coke may be 
comparatively free from this noxious element even when made 
from a poor coal. Coke burns without flame and makes a 
fierce fire when forced. 

Lignite, or brown coal, is of more recent geological 
formation than coal, and is in a manner intermediate between 
coal and peat. It frequently contains much moisture and 
mineral matter. It is used where good coal is difficult to get, 
and while the better varieties form a useful fuel, the poorer 
qualities have little value. 

Peat, or turf, is obtained from bogs. It consists of 
slightly decayed roots of the swamp vegetation mingled with 
more or less earthy matter. For domestic use it is cut and 



50 STEAM-BOILERS. 

dried in the air. It is little used for making steam, though 
when pulverized, dried, and compressed it makes a useful 
artificial fuel. 

Wood is used for making steam either in remote places 
where coal is hard to get and timber is plenty, or where saw- 
dust or other refuse wood is produced in quantity in manufac- 
turing operations. Wood is also used for kindling coal-fires. 
One cord of hard wood is equivalent to one ton of anthracite 
coal ; one cord of yellow-pine is equal to half a ton of coal ; 
other soft woods are, as a rule, of less value for fuel. 

Charcoal is made by charring wood ; it is but little used 
for making steam. 

Mineral Oil, in the form of crude petroleum or the refuse 
heavy oil left from the distillation of petroleum, is used for 
making steam, especially in the neighborhood of the Black 
Sea oil-field, and by steamers carrying oil from those fields. 
It is customary to throw the oil into the furnace in the form 
of finely divided spray through special spraying apparatus 
worked either with compressed air or with superheated steam. 
The use of superheated steam has its convenience only to 
recommend it, for it adds to the inert material to be uselessly 
heated. Special precautions must be taken, when petroleum 
is burned, to avoid flooding the furnace with oil and to pre- 
vent explosions of the vapor and burning of the oil in tanks 
or receptacles. 

Gases. — Natural gas from gas-wells has been used for 
making steam, usually in a crude and wasteful way. Some 
attempts have been made to use gas made from poor and 
smoky coal, in producer-furnaces like those used in metallurgi- 
cal operations ; but the gain to be expected is only the sup- 
pression of the smoke nuisance, which is rather a social than 
an economical problem. 

Artificial Fuels. — The small waste from coals and char- 
coals, sawdust, and other fine combustible material which 
cannot be sold in such shape, is sometimes made into cakes or 



FUELS AND COMBUSTION. 51 

briquettes by mixing it with some adhesive material and then 
compressing it. The adhesive materials have been wood-tar, 
coal-tar, or else clay. Tar is available in limited quantities 
only, and clay is disadvantageous since it adds to the inert 
material, of which fine fuel is liable to have an excess. 
Artificial fuels have some advantages for special purposes, and 
can be stored compactly ; they are used mostly where good 
fuel is difficult to get. 

Composition and Heat of Combustion of Coals. — The com- 
position of American coals is given by three sets of tables : one 
by Mr. Henry J. Williams, page 57, gives the results of analyses 
made by him in 1897; a second table, pages 52 and 53, gives 
the analyses made at the coal testing plant of the United 
States Geological Survey; and a third table, pages 54 and 55, 
contains the results of analyses made by a number of chemists, 
and includes also the work of the U. S. Geological Survey. 

From this last table, which was given in a report of a committee 
on fuel supply appointed by the Boston Chamber of Commerce, 
the summary given on page 56 was made. 

The table on pages 54 and 55 has been made with the coals 
arranged in the order of the carbon hydrogen ratio. 

It will be noticed that the highest heating value of any 
of these coals occurs with a carbon hydrogen ratio of approxi- 
mately 18.7. 

As would be expected the coals with the larger percentage 
of ash show a smaller heating value. 

The tables on pages 54 and 55 and the summary on page 56 
give the average of a great number of analyses, and, in judg- 
ing of the heating value to be expected from any particular coal, 
these results may be depended upon with more certainty than 
the results of one or two analyses on a sample of that coal. 

It is to be noted also that heating values above 14,600 
B.T.U. are not numerous. 

The chemical analyses and heating values of a few foreign 
coals are given by Mahler in the table, page 58. 



52 



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FUELS AND COMBUSTION. 



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FUELS AND COMBUSTION. 



59 



Composition and Heat of Combustion of Petroleums. — The 
heat of combustion of petroleum is much higher than for coal. 
This is due largely to the greater amount of hydrogen contained 
in the petroleums. 

COMPOSITION OF PETROLEUMS. 





Carbon. 


Hydrogen. 


Oxygen. 


Specific 
Gravity. 


Heating 
Value, 
B.T.U. 




849 
86.3 
86.6 
87.1 


13.7 

13.6 
12.3 
11. 7 


1.4 

0.1 
1.1 
1.2 


0.886 
0.884 
0.938 
0.938 


20,736 




22,027 




20,138 




19.832 







PROPERTIES OF CRUDE AND FUEL OIL. 



Oil. 


Field. 


c 


•8 

O 


a 

M 

2 


c 

W 


a 
<v 

M 

>, 
X 




0. 






H 
pq 


Authority. 














. 9266 

0.9179 

. 9240 
0.9260 

0.9416 


I98 




18,460 
18,500 

19,060 
19.481 

18,513 


) Prof. A. C. Scott, 
) Univ. of Texas. 

) U. S. Naval Liquid 
) Fuel Board. 

Prof. W. C. Blasdale, 














Crude 
Fuel 


Beaumont, Tex.. . . 
Beaumont, Tex.. . . 

Whittier, Cal. . 


84.6 
833 


10.9 
12.4 


I.63 
O.50 


2.87 
3.83 


I80 
216 


200 
240 


















Univ. of California. 



Heat of Combustion. — The number of thermal units de- 
veloped by the complete combustion of one unit of weight of a 
fuel is called the heat of combustion. 

The heats of combustion of carbon in various forms as de- 



termined by Berthelot * are: 



Diamond 7859 calories 

Diamond bort 7860.9 calories 

Graphite 7901.2 calories 

Amorphous from wood 8137.4 calories 

* Comptes rendu, 1889. 



60 STEAM-BOILERS. 

The following table gives the heat of combustion of some 
elements and simple gases. 

Carbon burned to C0 2 8,140 calories; 14,650 B.T.U. 

Carbon burned to CO 4400 B.T.U. 

Hydrogen 34, 500 calories; 62,100 B.T.U. 

Sulphur 4,032 B.T.U. 

Marsh-gas, CH 4 23,513 B.T.U. 

Olefiant gas, C 2 H 4 2I >343 B.T.U. 

Carbon monoxide 4>393 B.T.U. 

Determination of Heat of Combustion. — The heat of com- 
bustion of any fuel, whether liquid or solid, may be determined 
by burning the fuel in a properly constructed calorimeter. The 
most recent and the best results are those obtained by the use of 
the type known as the Mahler bomb. This is a strong receptacle 
of wrought iron or bronze, gold-plated or enamelled inside. The 
fuel to be tested is placed in a small platinum crucible, with an 
arrangement for igniting by electricity. The bomb is then filled 
with oxygen under the pressure of about twenty-five atmos- 
pheres, and is placed in a calorimeter-can containing water. 
There is oxygen in excess, so that the charge when ignited is 
completely consumed, and the resultant total heat of combustion 
is absorbed by the metal of the bomb and by the water in the 
calorimeter. The corrections for the calorimeter are determined 
by burning in it some substance like cane sugar, for which the 
heat of combustion is known. The processes of making com- 
bustion determinations are simple and direct; the difficulties 
are those incident to accurate measurements of temperatures, 
for which purpose the best physical thermometers are required. 

Consulting engineers as a rule send the samples of coal on 
which they want determinations of the heat of combustion made 
to some expert chemist or physicist who may make a specialty 
of such work. 

There are many cases, however, where great accuracy in the 
determinations is not required, hence an expert operator is not 
needed. 



FUELS AND COMBUSTION. 6 1 

As a large and a constantly increasing number of manu- 
facturing establishments are now buying coal on the " heat-unit 
basis " and as the price of the coal is often fixed by its heating 
value, it becomes necessary to test samples from each carload of 
coal delivered. The number of samples to be tested becomes so 
large that it pays to install a complete outfit for coal testing. 

Such an outfit costs about $300 and can be operated by any 
skilled engineer. 

In the near future the determination of the heat of combus- 
tion of coal will be one of the regular duties of the chief engineer 
in charge of the operation of the power plant of an establishment. 
With this in mind it may not be out of place to give here in some 
detail a description of a coal calorimeter, its manipulation, 
standardization, and the method of making what calculations are 
needed in getting the heating value of a fuel. 

The cuts shown by Figs. 30 and 31 illustrate the Emerson 
Fuel Calorimeter, and are taken, as is also considerable of what 
follows, from a paper written by Mr. Emerson. 

The bomb, which is made of steel, consists of two cups joined 
by means of a heavy steel nut. The two cups are machined at 
their contact faces with a tongue and groove; the joint being 
made tight by means of a lead gasket inserted in the groove. 

The lining is of sheet metal, spun in to fit, or of a double- 
process high- temperature porcelain. 

The pan holding the combustible, shown at the centre of the 
bomb in Fig. 30, is made of platinum or nickel, and the support- 
ing wire of nickel. 

The jacket is a double-walled copper tank between the walls 
of which water is inserted. 

The calorimeter-can, which is as light as possible, is made of 
brass. 

The stirrer is directly connected to a small motor and is 
enclosed in a tube to facilitate its action in circulating the water. 
The stirrer is mounted on a post on the calorimeter jacket as is 
the thermometer holder. 




(62) 



Fig. 30. 



FUELS AND COMBUSTION. 



63 



The piping for the insertion of oxygen under pressure is fitted 
with a hand union at one end to make the connection with the 
bomb, and the other end has a special fitting, to fit the oxygen 
supply tank. 

In getting ready to make a determination of the heating 
value of a coal, one proceeds as follows: first, place the lower 
half of the bomb in the holder, shown at the left in Fig. 31, and 




Fig. 31. 

place also the shallow fuel pan in the wire support which holds 
it in the centre of the bomb. 

Twist one end of the fuse wire through the small hole at one 
edge of the fuel pan, leaving the short end of sufficient length to 
bend over the ring which supports the pan and make good con- 
tact with it. The long end of the wire is now extended across 
the fuel pan through a hole in a mica upright, shown in Fig. 30 
as the vertical piece at the left of the pan, and attached to the 



D4 STEAM-BOILERS. 

binding post on the side of the bomb. This wire is bent down 
into the pan so as to be in contact with the fuel charge but it 
must not touch the pan except at the point of connection. 

Next, fill a test-tube with the sample, which has previously 
been crushed and powdered, and weigh the same accurately to 
a tenth of a milligram. Pour from this into the pan of the 
bomb until the pan is approximately half full. Weigh the test- 
tube again, and the difference gives the net quantity of fuel in 
the bomb. This weight should be at least five tenths of a 
gram, and should not exceed 1.2 grams. 

Nineteen hundred grams of distilled water are now placed in 
the calorimeter-can at a temperature about one and one half 
degrees below the jacket temperature which should be about the 
same as that of the room. 

The bomb is next placed in the calorimeter and the stirrer 
and the thermometer are lowered into position. The thermome- 
ter is immersed about 3 inches in the water, care being taken 
that the bulb does not touch the side of the can. 

The terminals of the electric circuit used for firing are now 
attached as shown in Fig. 30. For hard coal the maximum 
charge should not be greater than one gram. Hard coal should 
not be as finely divided as soft coal: if the sample of hard coal 
passes through an 80-mesh sieve it is fine enough. 

The upper half of the bomb is next placed in position and the 
nut screwed down by the use of a long wrench. 

The bomb is now ready to be filled with oxygen through the 
attachment shown in Fig. 31. 

The spindle on the bomb need only be opened one turn and 
the amount let into the bomb may be regulated by the value on 
the oxygen tank. When 300 pounds is shown by the gauge the 
value on the tank is closed and the spindle screwed down. The 
hand wheel on this spindle is now removed. This spindle serves 
also as one of the terminals for the electric circuit. 

After filling the bomb with oxygen it should be tested for 
leaks by immersing same in a glass jar filled with water. Care 



FUELS AND COMBUSTION. 65 

bhould be taken not to tip the bomb lest some of the coal be 
spilled from the fuel pan. 

The stirrer is now started. After waiting three or four 
minutes for the temperature of the water and bomb to equalize, 
readings of the thermometer to yoVo or 2"oVo °^ a degree are 
taken at half-minute intervals for the next five minutes, when 
the firing switch is turned on for a second only. 

In a few seconds the temperature begins to rise rapidly and 
readings are taken as before, every half minute from the time of 
firing till the maximum temperature is reached, generally at an 
interval of less than six minutes' duration. 

After the maximum temperature is reached the rate of change 
of temperature is due only to radiation to or from the calorim- 
eter, and in order to make the corrections for this it is necessary 
to continue the readings at thirty second intervals for another 
five -minute period. 

The data obtained during the run is used as follows: 

The difference between the temperature at maximum and 
the temperature at firing gives the apparent rise in temperature 
in the calorimeter. To this apparent rise must be applied a 
cooling correction computed thus: 

The change in temperature during the preliminary five 
minutes of reading divided by the time (five minutes) gives the 
rate of change of temperature per minute due to radiation to or 
from the calorimeter and also any heating due to stirring, etc. 
This factor we will call Ri, in like manner the readings taken 
after final temperature give R 2 . The two rates of change of 
temperature give the existing conditions in the calorimeter at the 
start and at the finish of the run. Therefore, the algebraic sum 
of the two rates divided by two will give the mean (or average) 
value of the rate of change of temperature during the entire run 
due to radiations to and from the calorimeter. This value mul- 
tiplied by the time from firing to maximum will give the total 
cooling correction. The cooling correction thus determined has 
been found by long experience to be a very close approximation 



66 STEAM-BOILERS. 

to the radiation effects encountered when working under these 
above conditions. 

This latter quantity is either added to or subtracted from the 
apparent rise taken from the data of the run, accordingly as the 
balance of heat radiation is to the surroundings or from the sur- 
roundings. This is at once determined from an inspection of 
the data. 

Cooling correction is expressed: 

p ■ p 

— X time from firing to maximum temperature. 

The corrected rise of temperature divided by the weight of 
fuel used will give directly the rise per gram of fuel. 

The rise per gram times the weight of water plus the " water 
equivalent " will give the calories per gram of fuel. The calorie 
referred to is the amount of heat necessary to raise one gram of 
water one degree centigrade. 

The result in calories per gram of fuel multiplied by the factor 
1.8 gives the B.T.U. per pound of fuel. 

In the measurement of the heat of combustion of a fuel in 
a bomb calorimeter the immersed parts of the calorimeter, in- 
cluding the bomb, can, stirrer, etc., are carried through the same 
rise in temperature as the water. The amount of heat absorbed 
by these immersed parts for one degree rise in temperature is 
known as the " water equivalent." 

A set of observations as taken, together with the calculations, 
follow. 



September 17, 191 2. 
Run No. 2. 



Sample No. 728 (dried). 
Thermometer used, No. 2295. 
Weight of tube and coal = 7.9379 
Weight of tube and coal = 7.0713 

0.8666 gram 
Weight of water = 1900 grams. 



FUELS AND COMBUSTION. 
THERMOMETER READINGS. 



6 7 



Time, 
min. sec. 


Temperature. 


Time, 
min. sec. 


Temperature. 


Time, 
min. sec. 


Tempera- 
ture. 





20.348 


30 


2 1 . OOO 


II 


23.182 


30 


20.350 


6 


22 .600 


30 


23.178 


I 


20.352 


30 


22.900 


12 


23.174 


30 


20.356 


7 


23 . IOO 


30 


23.170 


2 


20.358 


30 


23.150 


13 


23 . 166 


30 


20.360 


8 


23 • 194 


30 


23. 162 


3 


20.362 


30 


23.196 Max. temp. 


14 


23-I58 


30 


20.364 


9 


23.196 


30 


23-154 


4 


20.368 


3° 


23-194 


15 


23.ISO 


30 


20.374 


10 


23-194 






5 


20.376 Firing temp. 


30 


23.190 







Apparent rise in temperature = 2.820. 

Rate of change of temperature before firing = 0.0056 = Ri. 

Rate of change of temperature after maximum temperature 
— 0.0088 = R 2 (taken between times 10 and 15). 

Average rate of change of temperature during run = 0.0016. 

Total cooling correction = (0.0016 X 3.5 (min.)) = 0.006 
(additive) . 

Total corrected rise in temperature = 2.826. 

Rise per gram of sample = 3.261. 

The water equivalent of bomb, calorimeter-can, stirrer, etc., 
= 490. 

Gram calories per gram of sample = (1900 + 490) X 3.261 

= 7794- 

British Thermal Units per pound of sample = 7794 X 1.8 

= 14,030. 

Note. Ri and R 2 are each for a five-minute period. The 
maximum temperature in the bomb was reached in 3.5 minutes. 

A bomb calorimeter when operating properly will give the 
true heat value of a given combustible if as a water equivalent 
factor we use that obtained from the weights and specific heats of 
the immersed parts, i.e., the sum of the products of the weight 
of each part times its specific heat. The testimony and the work 
of such physicists as Berthelot and Mahler have conclusively 



68 STEAM-BOILERS. 

proven that this above method is correct. It is sometimes 
desirable to check this value by burning a combustible of known 
calorific value. Extreme care should be taken that such stand- 
ardizing substances should be of practically ioo per cent purity 
and absolutely free from chemically or physically combined 
water. 

The value of such a standard substance in calories per gram is 
divided by the rise in temperature in the calorimeter per gram of 
sample and the result is the water plus the water equivalent of 
the apparatus. The water being known, the water equivalent 
is thus determined. 

With a combustible of absolute purity this determination 
will check the value of the water equivalent as figured from the 
weights and specific heat of the material included in the immersed 
parts of the calorimeter. 

Cane sugar may be obtained at the Bureau of Standards at 
Washington, D. C, in a high degree of purity, and is probably 
the most desirable substance available for standardization. 
(When burning sugar carbon in the bomb use 400 pounds per 
square inch pressure of oxygen.) Naphthalene, although fre- 
quently used, is uncertain in its action if burned in a powdered 
or flaky condition. Upon ignition it burns with extreme rapidity, 
frequently scattering the charge without burning the same. 
The best results are obtained from this latter material if it is 
previously melted into a capsule. Naphthalene volatilizes to 
such an extent that upon ignition of the charge the naphthalene 
vapor in some cases explodes or detonates, and this is undesirable 
as it introduces a possibility of injuring the bomb. Benzoic 
acid is also useful as a standardization agent. 

Sampling Coal. — The original sample taken from the coal 
pile, shipload, or carload shipments must be large. A large sample 
insures that we will get in the original sample, at least, one that 
is a fair average of the whole, provided the selections are made 
with due care. If we are taking a sample from a 5 00- ton ship- 
ment the original sample should be not less than one ton. 



FUELS AND COMBUSTION. 69 

The most convenient place to sample coal is under conditions 
where it is being handled, i.e., by bucket elevator, belt conveyor, 
team load, or car. Shovelfuls taken every so often from belt or 
bucket conveyor, a shovelful or two from every other team load 
during cartage and from carload shipments, several well selected 
shovelfuls from each car, in each case will give satisfactory 
results. In carload shipment the heavy pieces of rock and slate 
gradually work toward the bottom of the car and due considera- 
tion of this fact is necessary in proper sampling of the same. 
For the boiler-test sample the fireman is instructed to lay aside 
a shovelful during each stroke period. 

In the case of a large coal pile, shovelfuls, all the way from 
the top to the bottom of the pile and on different sides, should 
be taken. Selections should be made 18 inches or 2 feet 
below the surface of the pile. A considerable portion of the 
sample should be taken from the larger pieces which are invari- 
ably found at the bottom of the pile. If of considerable size the 
pieces should be broken and parts of the fragments retained 
in the sample. Pieces encountered which contain practically 
nothing but slate or other forms of rock should not in each and 
every case be included in the sample. It is largely a matter of 
observation of the apparent percentage of such material that 
governs the sampler as to how much of the same he shall include 
in his sample. His judgment in this matter determines partly 
the success or failure of his work. The intrinsic impurities of the 
coal will be included in proper proportions if the sampler exerts 
a reasonable amount of care. 

If sampling is done at the mine, several points should be 
chosen from a map of the mine, which will give a fair sample of 
the whole. These points should be near the working face. A 
cut across the face 6 inches in width and 1 inch in thickness 
should be made at each point. This cut should be taken out 
complete except that which would be rejected by the mine 
worker. The samples taken from the several points should be 
thrown together, crushed, mixed, and treated according to the 



70 STEAM-BOILERS. 

directions given below. In determining the quality of the 
average output of a mine the most convenient place to sample is 
from the cars as they come from the mine. 

The original sample is reduced in bulk and at the same time 
made to retain the same average quality by the process of 
quartering. The sample is spread out on an oilcloth, canvas, or 
smooth floor and thoroughly mixed by overhauling with a shovel. 
The large pieces should be crushed until the maximum is not 
greater than the size of an egg. Lines are drawn through the 
sample at right angles, thus dividing it into quarters. Two 
opposite quarters are taken out and the rest rejected. The part 
retained is again mixed, crushed, and requartered. In this man- 
ner the size of the sample is reduced and we do not destroy the 
average quality if our mixing is reasonably thorough. The 
maximum size of the pieces should be reduced as we decrease the 
size of the sample. Careful and thorough mixing is the first 
essential in this process of quartering. The crushing is usually 
done with a sledge or maul. The sample is reduced until about 
sufficient to fill a two-quart jar. 

This sample is run through a grinder and requartered after 
mixing on glazed paper or oilcloth, with repetitions of the same 
until the sample is reduced to about 40 grams. 

This ultimate sample is powdered with fine grinder or mortar 
and pestle until it passes completely through an 80-mesh 
sieve. The sample is immediately placed in a sealed bottle 
ready for test. 

Throughout the process of sampling, care should be taken 
that the sample shall not be long exposed to the air, as con- 
siderable moisture will be lost. 

The Purchase of Coal on Specifications. — During the past 
few years a great many coal consumers have taken up the pur- 
chase of coal on specifications with varying degrees of success. 
In this, as in most new movements, some difficulties have been 
encountered, and the results have not been satisfactory in every 
case. The principal reasons for failure have been in the appli- 



FUELS AND COMBUSTION. 7 1 

cation of the method rather than in the method itself. Many 
misunderstandings have arisen on the one hand because the pur- 
chasers are prone to expect too much, to take faulty samples, or 
to act on inaccurate analyses of the coal delivered, and on the 
other hand because the coal companies are inclined to overesti- 
mate the excellence of coal they are able to deliver. 

The general method of buying coal on specifications is for 
the purchaser to ask for bids, to be based upon the delivery of 
coal of a specified analysis, allowing certain variations for the 
B.T.U. and the various constituents. Should the analysis show 
variations from the specifications, premiums are paid or penalties 
exacted in proportion to such variations above or below the 
standard. In some forms of specifications the bidder submits 
an analysis of coal he proposes to deliver, and the analysis of the 
successful bidder is taken as a standard for the contract. In 
some contracts the adjustment of price is based on the moisture, 
volatile, ash, sulphur, and B.T.U., while in others only the ash 
and B.T.U. are considered. 

The B.T.U. should always be one of the factors, as steam 
coal is purchased for the heat which may be developed from it. 

Moisture is also of great importance, as it represents so much 
valueless material; it should be ascertained when the selling 
weights are obtained. 

Volatile has two objectionable features: first, the production 
of smoke; second, reduction in boiler efficiency. These may be 
overcome by proper boiler installation and careful firing with a 
view to complete combustion. In the absence of these condi- 
tions it is best to avoid high volatile coals. It seems that the 
lower boiler efficiency due to higher volatile coals has been 
greatly overestimated, for the results of some 400 boiler tests, 
made by the United States Geological Survey, indicate that the 
boiler efficiency is about 2 per cent lower with coal containing 
35 per cent volatile than it is with coal of 15 per cent volatile.* 

* Report by the Committee on Fuel Supply of the Boston Chamber of Com- 
merce, November, 1909. 



72 STEAM-BOILERS. 

Ash affects both the capacity and the efficiency of a boiler, 
and the price of coal should vary with it. Ash not only replaces 
combustible material, but also reduces the efficiency of the boiler 
by clogging the grate, by carrying unburned coal with it to the 
ash-pit, and by its accumulation on the heating surface causes 
additional labor and extra expense for its removal. 

Sulphur in excess is penalized because its presence is believed 
to be a general indication of clinkering properties in coal. This 
indication is not always correct, as fluxing materials other 
than those accompanying sulphur are usually contained in ash. 
The average method of analysis does not, however, deter- 
mine these qualities, nor is it usually worth while to determine 
them. 

There is much diversity of specifications, even for similar 
coals and similar plants, and there is need for some standardiza- 
tion of their form as well as the method of their application. 

Coal Specifications. — Two forms of specifications are given 
below. The first one was drawn for the Massachusetts Insti- 
tute of Technology. This calls for a high-grade coal, like a 
Pocahontas or the best of what is known as New River coal. 

" Coal must be of a good quality of bituminous steam coal, 
free from dirt. A fair proportion of the coal is to be in the form 
of lumps. Analysis of the dry coal shall not show more than 
22 per cent volatile matter, 7 per cent ash, 1^ per cent sulphur, 
and the calorific value shall not fall below 14,500. The coal is 
to contain less than 3 per cent of moisture. 

" The samples of coal shall be taken by the Institute or its 
representative and no other sample will be recognized. The con- 
tractor or his representative may witness the operation of the 
sampling if so desired. Samples of the coal delivered will be 
taken by the Institute or its representative as the coal is being 
delivered. The original sample shall be taken from the wagons 
while being unloaded. Two or more shovelfuls of coal shall be 
taken from each wagon load sampled, and at least three wagon 
loads will be represented in any one sample. The sample shall 



FUELS AND COMBUSTION. 73 

be thoroughly mixed and quartered in the usual manner. The 
final sample is to be pulverized and passed through an 80-mesh 
sieve. A part of the final sample shall be put aside in an air- 
tight jar properly marked, for the contractor, so that he may 
verify results if he so desires. 

" The coal shall be tested by the Institute or its representa- 
tive, a bomb calorimeter being used. Should the contractor 
question the results, a sufficient quantity of the original sample 
is to be furnished him for testing if he so requests it. Should the 
heating value per pound of dry coal fall below 14,500 heat units, 
or should the moisture exceed 3 per cent, or the ash exceed 
7 per cent, or the sulphur i| per cent, this contract may be ter- 
minated at the option of the Institute. 

" The contractor agrees to furnish coal to conform to the 
above specifications at a price of $ . . . per ton of 2000 pounds 
of coal." 

Another form of contract reads: 

" Coal shall be bituminous or semi-bituminous, of good 
quality free from excessive amount of foreign matter. Each 
bidder shall state in his proposal the standard heating value in 
British thermal units per pound of dry coal that he proposes to 
furnish and shall also give an analysis of it, showing the per- 
centage of moisture, volatile matter, ash, and sulphur. 

" The calorific value and the analysis of the coal of the 
accepted proposal shall be a part of the contract. The price 
and the heating value shall be used to compute the cheapest coal. 
Consideration, however, shall be given to the quality, and the 
company shall reserve the right to make award according to its 
best interest. 

" Samples of the coal shall be taken by the company. The 
samples shall in no case be less than 100 pounds, and shall be 
carefully selected so as to represent a fair average of the whole. 
No other sample will be recognized. The samples shall be re- 
duced by thoroughly mixing and quartering until a final sample 
is obtained for testing, which shall at once be placed in an air- 



74 STEAM-BOILERS. 

tight jar or can and sealed for moisture determination. The 
contractor or his representative may be present to witness the 
operation of sampling. 

" The test shall be made by the company according to the 
method adopted by the American Chemical Society, using a 
bomb calorimeter. 

" Payments shall be made on the basis of price and analysis 
named in the proposal corrected for variations in moisture, ash, 
and calorific values as follows: 

" Deductions shall be made from the contract price at the rate 
of 2 cents per ton for each whole per cent of moisture above 
the contract specification. 

" Deductions shall be made from the contract price at the 
rate of 2 cents per ton for each whole per cent of ash above 
the limit specified in the contract. 

" Deductions shall be made from the contract price at the 
rate of 1 cent for each 50 B.T.U. which the coal develops less 
than the standard specified in the contract. 

" The company shall have the right to reject any coal having 
more than 22 per cent volatile matter, 10 per cent ash, 1.5 per 
cent sulphur, and a calorific value of more than 500 B.T.U. less 
than the standard specified in the contract, and the contractor 
shall remove the same at his expense." 

Volume of a Ton of Coal. — 

Kind of Coal. Cubic Feet to Ton. 

Soft coal 41 to 43 

Buckwheat or pea 37 

Nut 34 

Furnace size 36 

Coke 76 

Volume of a Ton of Ash. — 

Cubic Feet to Ton. 

Ash not packed 43 to 50 



FUELS AND COMBUSTION. 



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76 STEAM-BOILERS. 

Chemistry of Combustion. — Calculations concerning the heat 
of combustion of fuels and the amount of air needed for com- 
bustion require a knowledge of the elements of chemistry. 

Elementary chemical substances are those that have not been 
decomposed, such as oxygen, hydrogen, and nitrogen. The ele- 
ments enter into chemical combination in fixed proportions by 
weight; these proportions are called the combining weights or 
the atomic weights of the elements. In the table on page 75 are 
given the most important chemical elements of fuels, their chemi- 
cal symbols, and their atomic weights. The table gives other 
useful information which will be referred to later. 

A chemical combination such as water is represented by 
a formula consisting of the symbols of the elements entering 
into the combination, each symbol having a subscript which 
shows the number of times the combining or atomic weight of 
the element occurs in the combination. Thus, water is repre- 
sented by H 2 0, 

which indicates that water is made up of two portions of hy- 
drogen and one portion of oxygen. It is commonly said that 
two atoms of hydrogen and one atom of oxygen unite to form 
one molecule of water. As the atomic weight of hydrogen is I 
and the atomic weight of oxygen is 16, we have water formed 
of two pounds of hydrogen to 16 pounds of oxygen. 

Again, carbon may unite with one portion of oxygen to 
form carbon monoxide or carbonic oxide, represented by CO ; 
or carbon may unite with two portions of oxygen to form 
carbon dioxide or carbonic acid, represented by C0 2 . Re- 
ferring to the table on page 60, it appears that the complete 
combustion to C0 2 gives more than three times the heat ob- 
tained from incomplete combustion to CO. But the resulting 
gas, C0 2 may be burned with one more portion of oxygen, and 
will finally form CO2. Assuming that the double process will 
yield the same amount of heat per pound of coal as is ob- 
tained by direct combustion to C0 2 , we may calculate the heat 
of combustion of one pound of carbon monoxide as follows: 



FUELS AND COMBUSTION. 77 

In the combustion of carbon to CO, 12 pounds of carbon 
unite with 16 pounds of oxygen, forming 28 pounds of CO, 
hence one pound of carbon will form 

5 = 2i lbs. of CO. 



12 

The heat developed by burning these 2 J- pounds of carbon 
monoxide, under our assumption, is 

14650 — 4400 = 10250 B. T. U., 

so that each pound of carbon monoxide will yield 

10250^21 = 4393 B. T. U., 

as given in the table on page 54. 

The complete combustion in either case will give 

12 -f 2 X 16 _ 2 

pounds of carbon dioxide for each pound of carbon. 

Calculation of Heat of Combustion.— If a fuel were a 
mechanical mixture of two chemical elements such as carbon 
and sulphur, the heat of combustion could obviously be found 
by calculating the parts separately and adding the results. For 
example, a mixture of 60 per cent carbon and 40 per cent 
sulphur would give 

0.60 X 14650 = 8790.0 
0.40 X 4032 = 1612.8 

10402.8 B. T. U. 

for each pound of the mixture. 

Fuels, as a rule, contain carbon in a free state, and various 
compounds of carbon and hydrogen, and compounds of carbon, 
hydrogen, and oxygen. Now the rapid union of chemical ele- 
ments is usually accompanied by the evolution of heat, as in 



78 STEAM-BOILERS. 

the combustion of oxygen and hydrogen. Conversely, heat is 
required to break up a chemical combination. The com- 
bustion of a fuel is a complex process, usually involving some 
breaking up of chemical compounds and the union of chemical 
elements with oxygen ; the exact nature of the process is far 
from certain even when the real chemical compounds and ele- 
ments of which the fuel is composed are known. As a rule we 
know only the final analysis of the fuel and do not know the 
compounds which enter into it. For this reason the only 
true way of determining total heat of combustion is by experi- 
ment. Nevertheless it is customary and convenient to make 
a calculation of the total heat of combustion by an arbitrary 
method, when the real heat of combustion of a fuel has not 
been determined. 

Dulong proposed that the heat of combustion should be 
calculated on the assumption that the oxygen in the fuel and 
enough hydrogen to unite with it and form water, could be set 
aside as inert, and that the remainder of the hydrogen and all 
the carbon could be treated as free elements. From the com- 
position of water and the atomic weights of hydrogen and 
oxygen it is clear that each pound of oxygen will require 

2X1 i 



16 



of a pound of hydrogen. Dulong's method may therefore be 
expressed by the equation 

Total heat = 14,6500+ 62, 100 (H — £0) 

in which the letters C, H, and O represent the weights of car- 
bon, hydrogen, and oxygen in one pound of fuel. No con- 
fusion need arise because the letters are used with a different 
significance from that given them in chemical formulae. This 
equation does not give very satisfactory results. 



FUELS AND COMBUSTIOX. 79 

Mahler has proposed an empirical formula for finding 
heats of combustions which in French units is 

Total heat = 8 140 C + 34, 500 H — 3000 ( O + N), 

in which C, H, O, and N represent the weights of the ele- 
ments carbon, hydrogen, oxygen, and nitrogen in a kilogram 
of fuel. The result is in calories. 

In English units Mahler's equation becomes 

Total heat = 14,650 C + 62, 100 H — 5400 (O + N), 

in which the letters represent the weights of the correspond- 
ing elements in one pound of the fuel. The result is in 
B. T. U. This equation gives results that agree very well 
with Mahler's experimental determinations, as shown by the 
table on page 58. 

For example, the total heat of combustion of Pittsburg 
bituminous coal, for which the ultimate analysis may be 
taken as 

= 0.7647, H = 0.0519, O — 0.0810, N = 0.0145, 

appears by Dulong's formula to be 

14650 C + 62, 100 (H — i O) 

= 14,650 X 0.7647 + 62, 100 (0.05 19 — ° - ° IO \ 

= 13,720 B. T. U. 

Mahler's formula for the same coal gives 

14,650 C + 62, 100 H — 5400 (O + N) 
= 14,650 X 0.7647 -f- 62, 100 X 0.05 19 

— 5400 (0.08 10 -|- 0.0145) 
= i 3 , 9 ioB. T. U. 

Air required for Combustion. — If the moisture and car- 
bon dioxide in the air be neglected, and if, further, the argon 



So STEAM-BOILERS. 

is not distinguished from the nitrogen, then we have for the 
composition of the atmospheric air, 

By weight |2 Xygen °' 232 

(Nitrogen 0.768 

( Oxygen 0.2094 

By volume ■< . T . T 

( Nitrogen o. 7906 

For rough calculations it is customary to consider that the 
atmosphere is made up of one volume of oxygen and four 
volumes of nitrogen. This approximation is sufficient for 
calculation of air required by fuels, and for similar purposes. 

The air required for combustion of a given fuel may be 
estimated from its composition and from the composition of 
the air. A few examples will make the process clear. 

Thus, carbon burned to CO, requires two portions of 
oxygen, so that one pound of carbon will require 

•£•_,! 

pounds of oxygen. Since air is 0.232 part oxygen by weight, 
one pound of carbon will require 

2$ -7- 0.232 = 11. 5 

pounds of air for complete combustion. 

In like manner one pound of hydrogen will require 

2 

pounds of oxygen, or 

8 -T- 0.232 = 34.5 

pounds of air for complete combustion. 

Another method of calculation is based on the approxi- 
mate composition of air, i.e., one volume of oxygen and four 
of nitrogen. This method depends on the fact that the 



FUELS AND COMBUSTION. 8 1 

weights of a cubic foot of different kinds of gases are propor- 
tional to their atomic weights ; so that if the weight of a cubic 
foot of hydrogen be taken for the basis 01 comparison and be 
called unity, then the weight of a cubic foot of oxygen will 
be 1 6, while that of nitrogen will be 14. We shall then have 
for the approximate composition of air one volume of oxygen 
having the weight 16, and four volumes of nitrogen having each 
the weight 14. In order to get one pound of oxygen we 
must take 

(16 + 4 X 14)^- 16 = 4J 

pounds of air. 

It has already been shown that one pound of carbon will 
require 2§ pounds of oxygen. By the method just stated it 
appears that a pound of carbon will require 

2| X 4i = 12 

pounds of air. This result is often quoted and is easily 
remembered. 

Since a pound of hydrogen requires 8 pounds of oxygen, 
this method gives 

8 X A\ = 36 

pounds of air for each pound of hydrogen. 

In calculating the air required for a fuel it is customary to 
use the convention proposed by Dulong for finding heat of 
combustion, namely, that each pound of oxygen in the fuel 
renders one eighth of a pound of hydrogen inert, and that the 
remainder of the hydrogen and all the carbon can be treated 
as free elements. In using this convention it is customary to 
take the approximate weights of air just calculated for a 
pound of carbon and a pound of hydrogen. The convention 
can then be stated in the form of an equation as follows: 

Air per pound ot tuel = 12 C + 36 (H — -JO), 



82 STEAM-BOILERS. 

In which the letters C, H, and O represent the weights of 
carbon, hydrogen, and oxygen in one pound of the fuel. 
An application of this equation to Pittsburg coal gives 

a- <- . J 0.08 io\ 
Air = 12 X 0.7647 -f- 36(0.0519 — ) = 10.7 pounds. 

This result is somewhat larger than would be obtained were 
the more exact composition of the atmosphere given on page 
59 used, together with the assumption that the oxygen ren- 
ders inert its equivalent of hydrogen ; but the method is not 
sufficiently well grounded to warrant much refinement. 

As a further illustration of the method the following cal- 
culation of the air required for one pound of defiant gas may 
be interesting. This gas, having the composition C a H 4 , con- 
sists of 

2 X 12 6 

— ■ = — carbon, 

2 X 12+4X 1 7 

hydrogen, 



2 X 12 + 4X 1 7 
and will require 

f X 12 -f- t X 36 = 1 5.4 pounds of air. 

Air for Dilution. — In order to secure complete combustion 
of coal in the furnace of a boiler it is necessary to supply an 
excess of oxygen, or, what amounts to the same thing, an 
excess of air. This excess varies from one half the quantity 
required for combustion to an equal quantity. Thus, roughly, 
from 18 to 24 pounds of air may be furnished per pound of car- 
bon and from 54 to 72 pounds of air per pound of hydrogen. 

Volume of Air for Combustion. — The table on page 75 
gives the density or weight of one cubic foot of the several 
gases mentioned, also the reciprocal of the density or the 
volume occupied by one pound of the gas. This is called the 
specific volume of the gas. The specific volume of air is 
12.39 at the pressure of the atmosphere and at the temper- 



With 50 per 
cent Dilution. 


With 100 per 
cent Dilution. 


225 


300 


675 


9OO 



FUELS AND COMBUSTION. 83 

ature 32 F. The volume of a pound of gas increases as the 
temperature rises. At 6o° F. one pound of air will occupy- 
about 13 cubic feet. To find the volume of air required per 
pound of fuel we may simply multiply the weight by 13, for 
ordinary calculations. Thus we shall have for the air per 
pound of the principal elements in fuels: 

Without 
Dilution. 

Carbon 150 

Hydrogen 450 

These approximate values are sufficient for determining 
the dimensions of doors or passages through which air is 
supplied to the fire. 

This method applied to Pittsburg coal will give, approxi- 
mately, 

10.7 X 13 ■■= 139 

cubic feet of air for each pound of coal without dilution. 
With dilution of 50 per cent the air required will be about 
210 cubic feet for each pound. 

Sometimes, in connection with boiler-tests or for other 
purposes, a more exact estimate of the amount of air is de- 
sired. The calculation for this purpose can be best explained 
by aid of an example. 

Example. — Required the weight and volume of air needed 
for combustion of Pittsburg coal with 50 per cent dilu- 
tion, the temperature of the atmosphere being yo° F. and 
the height of the barometer being 29 inches, when reduced 
to 32 F. 

This coal is composed of 76.47 per cent carbon, 5.19 per 
cent hydrogen, and 8.10 per cent oxygen. Assuming that 
the oxygen renders inert one eighth of its weight of hydrogen, 
there will be available 

5. 19 = 4. 18 per cent 

o 



84 STEAM-BOILERS. 

of hydrogen and 76.47 per cent of carbon. Since one pound 
of carbon requires 2§ pounds of oxygen, and one pound of 
hydrogen requires 8 pounds, the weight of oxygen required 
per pound of coal is 

2f X 0.7647 + 8 X 0.0418 = 2.374 pounds. 

But air contains 23.2 per cent of oxygen by weight, so that the 
air required per pound of coal is 

2.374-^-0.232 = 10.2 pounds. 

The specific volume of air is 12.39, so tnat each pound of 
coal will require 

10.2 X 12.39 — I2 6 

cubic feet of air at the normal pressure of the atmosphere 
and at 32 ° F. 

To find the volume of air required at the actual pressure 
of the atmosphere and the actual temperature, we have the 
facts that the volume of a given weight of air is inversely pro- 
portional to the absolute pressure and directly proportional 
to the absolute temperature. Now the absolute pressure of 
the atmosphere is 29 inches of mercury as given by the 
barometer, while the normal pressure is 29.92 inches of mer- 
cury. To get the absolute temperature we add 459.5 t0 tne 
temperature by the thermometer; the absolute temperature of 
32 F. is 491.5, and that of 70 F. is 529.5. Under the con- 
ditions of the problem the air required per pound of fuel will 
have the volume, without dilution, of 

. 529.5 29.92 

126X^^X^^ = 140 
491.5 29.00 

cubic feet. With 50 per cent dilution the volume will be 210 
cubic feet. 

Determination of Air per Pound of Coal. — The amount 
of air supplied per pound of coal may be determined either by 



FUELS AND COMBUSTION. 85 

measuring the air supplied to the furnace or by an analysis of 
the products of combustion. 

For the first method the following arrangement has been 
used in boiler-tests at the Massachusetts Institute of Tech- 
nology: The ash-pit doors are removed and a sheet-iron 
mouthpiece is fitted over the opening into the ash-pit. The 
air for combustion is supplied by a cylindrical sheet-iron con- 
duit leading into this mouthpiece. The area of the conduit 
should be at least equal to the area of the fire-door or fire- 
doors, and its length should be several times its diameter. 
The velocity of the air in the conduit is measured by an ane- 
mometer, from which the volume of air is readily calculated, 
and its weight determined from the temperature and pressure of 
the atmosphere. The joint between the mouthpiece and the 
furnace front must be luted to avoid leakage, and leaks or ad- 
mission of air to the furnace otherwise than through the sheet- 
iron conduit must be stopped or allowed for Anemometers, 
even when tested and rated, are liable to be affected by errors 
of two per cent or more. They are commonly tested by 
swinging them on a revolving arm through still air — a method 
that is proper for small or moderate velocities, but difficult to 
use, and is vitiated by the action of centrifugal force at high 
speeds. An ideal way of testing an anemometer would be to 
find its reading in such a conduit when the weight, and con- 
sequently the velocity, of the air per second is known. The 
weight may be determined by causing the supply of air to 
flow through a well-rounded orifice, to which calculations by 
the proper thermodynamic equations may be applied. This 
method for large conduits would involve the use of a very large 
air-compressor, which makes it hardly practicable. 

Orsat's Gas Apparatus.— This apparatus, which is well 
adapted to the analysis of flue-gases, determines the propor- 
tion by volume of the carbon dioxide, carbon monoxide, and 
oxygen in a mixture of gases. The remainder of tne flue- 
gases is commonly assumed to be nitrogen, but it includes 



86 



STEAM-BOILERS. 



unburned hydrocarbon, if there be any, and steam or vapor 
of water. In Fig. 32, A, B, and Care pipettes containing, 
respectively, solutions of caustic potash to absorb carbon diox- 
ide, pyrogallic acid and caustic potash to absorb oxygen, and 
cuprous chloride in hydrochloric acid to absorb carbon mon- 
oxide. 

At Wis a three-way cock to control the admission of gas 
to the apparatus ; at D is a graduated burette for measuring 
the volumes of gas, and at P is a pressure-bottle connected 
with D by a rubber tube to control the gases to be analyzed. 
The pressure-bottle is commonly filled with water, but glyc- 




Fig. 32. 



erine or some other fluid may be used when, in addition to the 
gases named, a determination of the moisture or steam in the 
flue-gases is made. 

The several pipettes A, B, and C are filled to the marks a, 
b, and c with the proper reagents, by aid of the pressure-bottle 
P. With the three-way cock W open to the atmosphere, the 
pressure-bottle P is raised till the burette D is filled with 
water to the mark m\ communication is then made with the 
flue, and by lowering the pressure-bottle the burette is filled 
with the gas to be analyzed, and two minutes are allowed 
for the burette to drain. The pressure-bottle is now raised 
till the water in the burette reaches the zero-mark and the 



FUELS AND COMBUSTION. 87 

clamp k is closed. The valve W 'is now opened momentarily 
to the atmosphere to relieve the pressure in the burette. Now 
open the clamp k and bring the level of the water in the pres- 
sure-bottle to the level of the water in the burette, and take 
a reading of the volume of the gas to be analyzed ; all readings 
of volume are to be taken in a similar way. Open the cock 
a and force the gas into the pipette A by raising the pressure- 
bottle, so that the water in the burette comes to the mark m. 
Allow three minutes for absorption of carbon dioxide by the 
caustic potash in A, and finally bring the reagent to the mark 
a again. In this last operation, brought about by lowering 
the pressure-bottle, care should be taken not to suck the 
caustic reagent into the stop-cock. The gas is again measured 
in the burette and the diminution of volume is recorded as the 
volume of carbon dioxide in the given volume of gas. In like 
manner the gas is passed into the pipette B, where the oxygen 
is absorbed by the pyrogallic acid and caustic potash ; but as 
the absorption is less rapid than was the case with the carbon 
dioxide, more time must be allowed, and it is advisable to 
pass the gas back and forth, in and out of the pipette, several 
times. The loss of volume is recorded as the volume of 
oxygen. Finally, the gas is passed into the pipette C y where 
the carbon monoxide is absorbed by cuprous chloride in hydro- 
chloric acid. 

The solutions are as follows : 

A. Caustic potash, 1 part ; water, 2 parts. 

B. Pyrogallic acid, 1 gramme to 25 c.c. caustic potash. 

C. Saturated solution of cuprous chloride in hydrochloric 

acid having a specific gravity of 1.10. 



are- 



The absorption values per cubic centimetre of the reagents 

A Caustic potash absorbs 40 c.c. carbon dioxide. 

B. Pyrogallate of potassium absorbs 22 c.c. oxygen 

C. Cuprous chloride absorbs 6 c.c. carbon monoxide. 



88 STEAM-BOILERS. 

Samples of gas for analysis by Orsat's apparatus should be 
taken from the back of the furnace, from the uptake, and from 
the chimney; the difference in composition of gases at the 
several points will give the basis for calculations of leakage. 

When it is not convenient to draw gases from the flue di- 
rectly into the measuring burette of the apparatus, samples of 
gas may be drawn into glass bottles with rubber stoppers, from 
which gas can be supplied to the burette. 

Calculation from a Gas Analysis. — The calculation of the 
amount of air supplied per pound of carbon and per pound of 
coal, from the known chemical constituents of the flue-gases, 
is best shown by an example. 

Example. — Let it be assumed that the analysis of the flue- 
gases resulting from the burning of Pittsburg bituminous coal 
gives by volume 13 per cent of carbon dioxide, 0.5 per cent 
of carbon monoxide, and 6 per cent of oxygen. It is con- 
venient to treat the percentages by volume as the number of 
cubic feet of the several gases in one hundred cubic feet of flue- 
gas. We will thus have — 

Density. 
Gas. Volume. (See page 5 5-) Weight. 

Carbon dioxide 13 0.12345 1.6043 

Carbon monoxide 0.5 0.07806 -0.03903 

Oxygen „ 6 0.08928 0.53568 

Now one pound of carbon dioxide is composed of 

2 X 16 $_ 

12 -f- 2 X 16 11 

of a pound of oxygen and 3/1 1 of a pound of carbon, and a 
pound of carbon monoxide is composed of 

16 _ 4 
12 -)- 16 ~~ 7 

of a pound of oxygen and 3/7 of a pound of carbon. Conse- 
quently we have. 



FUELS AND COMBUSTION. 89 

ft X I.6043 = I- 1668 ft X I.6043 =0.4375 

4 X O.03903 = O.0223 f X O.03903 = O.O167 

0.5357 



Pounds of oxygen, 1.7248 Pounds of carbon, 0.4542 

And as air consists of 0.232 part by weight of oxygen, the air 
per pound of carbon from the gas analysis is 

_lZ_z — 1_ 0.232 = 16.4 pounds. 
0.4542 

The coal in question contains 76.47 per cent of carbon, 5. 19 
per cent of hydrogen, and 8. 10 per cent of oxygen. Of these 
elements Orsat's apparatus accounts for the carbon only ; the 
oxygen and hydrogen together with unburned volatile matter 
pass off with the nitrogen. 

The analysis shows 16.4 pounds of air for each pound of 
carbon ; consequently the carbon in one pound of coal will 

require 

0.7647 X 16.4 = 12.5 

pounds of air. Assuming that the oxygen in the coal renders 
one eighth of its weight of hydrogen inert, and that the re- 
mainder will require 36 pounds of air per pound of hydrogen, 
we shall have 



,/ 0.08 io\ 
36(0.0519 — ) = 1.5 



of a pound of air required for the hydrogen. So that the 
total air per pound of coal is about 

12.5 + l 'S = l 4 pounds. 

The calculation just given, involving the use of the densities 
of the several gases, is perhaps the most readily understood ; 
there is another method, which gives the same result and is 
more expeditious, depending on the fact that the weight of a 
gaseous compound referred to hydrogen as unity, is half its 



90 STEAM-BOILERS. 

molecular weight. This quantity is called the vapor density of 
the compound. 

Thus the vapor density of carbon dioxide, C0 2 , is 

£(12 +2x16) = 22; 

and the vapor density of carbon monoxide, CO, is 

1(12 + 16) = i 4 . 

Assuming as before that in each 100 cubic feet of flue-gases 
there are 13 cubic feet of C0 2 , 0.5 of CO and 6.0 of O, we 
have for the corresponding weights, based upon hydrogen as 
unity, 

13 X 22 = 286 for CO a 

0.5 X 14 = 7 for CO 

6.0 x 16 = 96 for O 

Total, 389 

The last result depending on the fact already noted, that the 
weights of elementary gases are proportional to the atomic 
weights. 

Now each pound of C0 2 contains 3/1 1 of a pound of carbon, 
and each pound of CO contains 3/7 of a pound of carbon, so 
that of the 286 parts by weight of C0 2 we shall have 

T 3 T X 286 = 78 

parts of carbon, and of the 7 parts by weight of CO we shall 
have 

tX7 = 3 
parts of carbon. The total weight of carbon will be 

78+3 = 3i. 
The weight of oxygen is clearly 

389-81 = 308. 



FUELS AND COMBUSTION. 91 

The oxygen per pound of carbon is therefore 

308^81 = 3.80, 

and the air per pound of carbon is 

308 . 

— ^-0.232 = 16.4 

pounds, as found by the previous calculation. 

Loss from Incomplete Combustion. — The presence of 
even a small amount of carbon monoxide in flue-gases is evi- 
dence of a very appreciable loss of efficiency, as may be seen 
by the following example, quoted from a test made on a 325- 
horse-power boiler at Lowell. The coal used was George's 
Creek Cumberland, fired by hand. 

An analysis of flue-gases by Orsat's apparatus showed 12.5 
per cent of CO,, 1. 1 per cent of CO, and 6.4 per cent of O, 
by volume. 

Using the method of vapor densities for making the calcu- 
lation, it appears that the CO a contained 

T 3 T x 12-5 X 22 = 75 parts of carbon, 

and the CO contained 

f X 1.1 X H = 6.6 parts of carbon. 

Now 75 pounds of carbon burned to C0 2 gives 

75 X 14,650 = 1,098,750 B. T. U., 

and 6.6 pounds of carbon burned to CO gives 

6.6 X 4400 = 29,040 B. T. U., 

or a total for all the carbon of 1, 127,790 B. T. U. 

Had all the carbon been burned to CO, , the heat of com 
bustion would have been 

(75 + 6.6) 14,650 = 1, 195,440 B. T. U. 



9 2 STEA M -BOILERS . 

The loss by incomplete combustion was consequently 

1,195,440—1,127,790 . 

— X 100 = 5.6 per cent. 



1,195,440 

The actual loss may be placed at a little less figure than 5.6 
per cent, since less air is required for burning carbon to CO 
than for CO„. 

Loss from Excess of Air. — The ideal condition would be 
to supply just enough air to burn all the carbon in the coal to 
C0 2 and all the free hydrogen to H 2 ; it is necessary to use 
somewhat more air than required for complete combustion to 
avoid the formation of CO and the attendant loss of heat. On 
the other hand, too great an excess of air occasions a loss, as 
that excess must be heated to the temperature in the chimney. 

As an example, suppose that Pittsburg coal can be com- 
pletely burned with 50 per cent excess of air, but that 100 per 
cent excess is allowed to pass through the grate. 

To simplify the problem we will neglect the effect of sul- 
phur and of the ash, more especially as it is not certain what 
their effect is ; we know only that it cannot be very impor- 
tant. 

Each pound of carbon will yield 3§ pounds of CO, and 
each pound of hydrogen will yield 9 pounds of H a O. There 
will therefore be 

3f X 0.7647 = 2.8039 pounds of C0 2 ; 
9X0.0519 = 0.4671 " " H 2 0. 

In the calculation for the weight of air (page 84) it has 
been shown that 2.374 pounds of oxygen and 10.2 pounds of 
air are required for combustion. There is therefore 

10.2 — 2.374 = 7.826 

pounds of nitrogen in the air for combustion. But each 
pound of coal contains 0.014 of a pound of nitrogen, so that 
the total nitrogen is 7.840 pounds. 



FUELS AND COMBUSTION. 93 

Now the heat required to raise the temperature of one 
pound of a substance one degree, called the specific heat, is 
given in the table on page 75. For carbon dioxide the specific 
heat is 0.2169, and the heat required to raise 2.8039 pounds 
one degree is 

2.8039 X 0.2 169 = 0.6082 B. T. U. 

The following are the calculations for the several compo- 
nents of the products of combustion : 

Weight. s P eci t fic 

s Heat. 

Carbon dioxide, C0 2 2.8039 X 0.2 169 = 0.6082 B. T. U. 

Steam, H a O 0.4671 X 0.4805 = 0.2244 " 

Nitrogen 7.840 X 0.2438 = 1. 91 14 " 

Air for dilution 50$.... 5.100 X 0.2375 = 1.2 112 " 



Total 3-9552 



u 



If the external air is at 6o° F., and the gases in the chim- 
ney are at 560 F., then the heat in the chimney-gases above 
the temperature of the air is 

500 X 3.9552 = 1978 B. T. U. 

The total heat of combustion of this coal by Dulong's 
formula is 13800 B. T. U. ; of this about 10 per cent will be 
lost by conduction and radiation. There will then remain to 
be transferred to the water in the boiler 

13800 — (1380 + 1978) = 10442 B. T. U. 

This is about 76 per cent of the heat generated by combus 
tion. 

Suppose that the dilution is allowed to be 100 per cent, 
so that 5 additional pounds of air per pound of coal are ad- 
mitted to the grate. Then to the above total must be added 



94 STEAM-BOILERS. 

1.2112 B.T. U., making in all 5.1664 B. T. U. Multiply- 
ing by 500, the difference of temperature assumed 

500 X 5- 1664 = 2583 B. T. U. 

Assuming, as before, 10 per cent for loss by radiation and 
conduction leaves 

13800 - (1380 + 2583) = 9837 B. T. U. 

to be transferred to the water in the boiler. This is about 72 
per cent, so that the loss by the excess of dilution is about 4 
per cent. 

Hypothetical Temperature of Combustion, — A calcula- 
tion is sometimes made of the temperature of the fire on the 
assumption that the total heat of combustion is all applied to 
raising the temperature of the products of combustion, includ- 
ing the ash. In the case of Pittsburg coal it has been found 
that 3.9552 B. T. U. are required to raise the products of 
combustion one degree, allowing 50 per cent for dilution. 
This coal has J. 6 per cent ash, for which a specific heat of 0.2 
may be allowed. We must therefore add to the total just 
quoted 

.076 X 0.2 = 0.0152 B. T. U., 

making in all 3.9704 B. T. U. Dividing the total heat by 
this quantity, we get 

13800 4- 3.9704 = 3480 F. 

for the elevation of temperature. To this we will add the 
temperature of the air admitted to the furnace, say 6o° F., 
making 3540 F. for the hypothetical temperature of the 
fire. 

Such a temperature is never reached in the furnace of a 
boiler, for the combustion is not instantaneous and is not 
completed in the furnace, as flames commonly extend over 



FUELS AND COMBUSTION. 95 

the bridge-wall or into the combustion- chamber; meanwhile 
there is an energetic radiation from the glowing fuel and 
flame, and a rapid transfer of heat from the hot gases to the 
heating-surface of the boiler. The better the fuel and the 
higher the hypothetical temperature of the fire the less chance 
is there that the actual temperature will approach it. 

In general the temperature in a furnace ranges between 2000 
and 2600 F., when the boiler is running at its rated capacity. 

Decomposition of Steam. — Among the many devices gotten 
up either to increase the efficiency of a boiler, to increase its 
capacity, or to raise the temperature of the furnace, there is a 
class claiming to operate through the decomposition of steam. 
The hydrogen, liberated by the supposed decomposition, burning 
in the presence of the oxygen also liberated by the supposed 
decomposition, would, on account of the high heating value of the 
hydrogen (62,100 B.T.U. per pound), furnish a large amount of 
heat. Two facts have been overlooked however. First, it is 
impossible to decompose steam in any appreciable quantity for 
any length of time at a temperature under 3500 F., a tempera- 
ture never reached in a coal furnace as used under boilers ; and 
second, that even if steam were decomposed at 3500 F. every 
pound of steam so decomposed would require at the instant of 
breaking up the " heat of reaction," 6900 B.T.U. per pound, and 
this value is just what is recovered by the burning of sufficient 
hydrogen to make one pound of steam. 

This is evident from the following: one pound of H unites 
with 8 pounds of O to make 9 pounds of H 2 0, and yields 
62,100 heat units; hence the heat per pound of steam formed is 
62,100 -f- 9 = 6900. The method of making hydrogen by pass- 
ing steam over heated steel chips depends upon the oxygen of 
the steam being absorbed by the iron of the chips in forming 
sesquioxide or black oxide of iron, thus liberating some hydro- 
gen. This action ceases after the oxide is once formed. 

The introduction of a jet of steam either over the grate, under 
the grate, or in the flue will, in most cases, increase the net capac- 



96 



STEAM-BOILERS. 



ity of a boiler, and in some cases the use of a steam jet over 
the fire as an aspirator or an air injector may, by bringing in an 
additional air supply immediately following a firing, prevent in- 
complete combustion and consequently make a slight net increase 
in economy after having deducted the steam used. 

C0 2 Recorders.— In many boiler plants continuous analyses 
or intermittent analyses are made of the flue gas by some form 
of automatic C0 2 recorder. 

The advantages of such analyses is evident from what has 
been said previously about the losses resulting from excess air 
or too little air supplied for combustion. 

The two makes of carbonic acid recorders most commonly 
used are the Uehling and the Sarco. 

Uehling C0 2 Recorder.— This instrument is continuous in 
its operation and the principle on which it operates may be 
illustrated by Fig. 33 • 

An aspirator D operated by a steam jet draws flue gas 
through two orifices ,4 and B of equal size. If the drop in pressure 




: ^ 



y 'tjuiy 






Fig. 33- 

caused by the aspirator action in the chamber C is constant, as 
shown by the height of the liquid in the leg q, there will necessarily 
be a drop in pressure in the chamber C, as shown by the height 
in the leg p, due to the fact that the same weight of gas is passing 
through each orifice. If, however, C0 2 be absorbed between 



FUELS AND COMBUSTION. 97 

the orifices A and B there will be less weight passing through B, 
and if the height of the liquid in the leg q remains constant the 
level in the leg p will change. 

The change of level of the liquid in the leg p serves to give 
an indication of the amount of C0 2 absorbed in the chamber C. 

The actual arrangement of the apparatus is shown diagram- 
matically by Fig. 34. 

A central receptacle of 8-inch pipe, 60 inches long, is nearly 
filled with water. The small central tube shown in the centre of 
this receptacle is open to the air at the top. 

The left-hand tube ends 6 inches above the lower end of the 
central tube, and the right-hand tube, shown dipping a few inches 
below the surface of the water, is just 48 inches above the lower 
end of the central tube. 

Opening the steam valve A allows steam to pass through the 
aspirator B and causes a drop in pressure in the small pipe lead- 
ing from B to the right-hand side of the cap on the top of the 
8-inch pipe. On opening the valve in this pipe a drop in pressure 
occurs in the top of the receptacle equal in amount to that re- 
quired to draw air from outside down through the water in the 
central tube, which, as has been said, is open to the air at its top 
end. At the same time flue gas is taken in through the pipe D 
into the chamber E, where it goes through a dust-removing filter, 
then through the pipes F and H, and any surplus gas not passed 
through the orifice K is drawn down through the left-hand tube 
in the receptacle and bubbles up through the water to the top, 
where it is removed by the aspirator. 

Beneath the aspirator B there is a chamber / through which 
the gas passes on its way to the orifice K and also on its return, 
after passing through the absorbent in the chamber L on its way 
to the exit orifice A r . By thus jacketing both pipes with the 
waste steam used by the aspirator the temperature of the gases 
entering either orifice is the same, 212 , no matter what the pres- 
sure of the steam supplied to the aspirator may have been. 

The pressure in the absorber L is transmitted through the 



STEAM-BOILERS. 



To Recording •■% 
Gage | 

— i JL 




Fig. 34. 



FUELS AND COMBUSTION. 99 

pipe M and its connections 55 either to a tube on the left reading 
per cent C0 2 or to a recording gauge. 

The absorbent may be either a dry carton changed once a 
week or a solution of caustic potash siphoned through L from 
the tank above. When a solution of caustic potash is used the 
absorber is rilled with pebbles or quartz, thus presenting a con- 
siderable amount of absorbing surface. 

Sarco C0 2 Recorder. — This recorder, shown by Fig. 35, auto- 
matically traps off, at regular intervals, 100 c.c. of gas from a 
continuous stream of gas. This trapped-off portion of gas is 
brought into contact with caustic potash, which absorbs the C0 2 , 
and a record is then automatically produced on a chart showing 
the amount of C0 2 in the respective samples of gas. 

Gas is drawn through the machine after passing through the 
filter and through the intake pipe D, at the right. The suction 
necessary to draw the gas through the apparatus is obtained by 
means of a jet of water falling from an overhead water supply 
tank, and passing through the ejector Q attached to the top of 
the recorder cabinet by means of a standard T. 

After actuating the ejector Q a portion of the water flows 
to the small tank L, which serves as a pressure regulator, and 
is provided with an overflow tube R. From this tank the water 
enters tube H in a fine stream, the strength of which is adjusted 
by the cock 5 (according to the number of records that may be 
desired per hour), and gradually fills the vessel K. 

Vessel K contains an ebonite float into which tube H admits 
falling water and from which siphon G extends. 

The water which enters K gradually fills it and compresses 
the air in the space above and surrounding the float. 

This pressure is transmitted to the solution of glycerine and 
water contained in lower part of K and forces it out into 
burette C. 

While this has been taking place the ejector Q has been 
drawing a continuous stream of gas right through D, C, and E 
in the direction indicated by the arrows. 



IOO 



STEAM-BOILERS. 




Fig. 35. 



FUELS AND COMBUSTION. IOI 

When the liquid rising in C has reached the inlet and out- 
let to this vessel, no further gas can enter the burette for the 
moment, and the ejector will now draw the gas through the seal 
F and out in the direction of the arrow for the time being. 

Before the liquid can close the centre tube in C the gas 
has to overcome the slight resistance offered by the rubber bag 
P and is therefore forced to assume atmospheric pressure. 

The moment the liquid has sealed the lower open end of this 
centre tube exactly ioo c.c. of the flue gas are trapped off in 
the outer vessel C and its companion tube, under atmospheric 
pressure. 

As the liquid rises further the gas is forced through the thin 
tube Z and into vessel A which is filled with a solution of 
caustic potash at 1.27 specific gravity. 

Upon coming in contact with the surface of the potash and 
the moistened sides of the vessel, the gas is freed from any car- 
bonic acid that may be contained in the sample, this being 
rapidly and completely absorbed by the potash. 

The remaining gas gradually displaces the potash solution 
in A, sending it up into vessel B. This has an outer jacket 
filled with glycerine and supporting a float N. Through the 
centre of this float reaches a thin tube through which the air in 
B is kept at atmospheric pressure. 

This float is suspended from the pen gear M by a silk cord 
and counterbalanced by the weights X. 

The liquid rising in B first forces a portion of the air therein 
out through the centre tube in the float and then raises the latter. 
This causes the pen lever to swing upwards, carrying the pen Y 
with it. 

The mechanism is so calibrated and adjusted that the pen 
will travel to the top, or^ero line, on the chart when only atmos- 
pheric air is passing through the machine and nothing is ab- 
sorbed by the potash in A . 

Thus, should any carbonic acid be contained in the gas sample 
it would be absorbed by the potash in A, not so much of this 



102 STEAM-BOILERS. 

liquid would be forced up into vessel B, and the float would not 
cause the pen to travel up so high on the chart, in exact accord- 
ance with the amount of C0 2 absorbed. 

When the liquid in C has reached the mark near the top of the 
narrow neck of that tube, the whole of the ioo c.c. has been forced 
on to the surface of the potash, one analysis being thus completed. 
At this moment the power water, which simultaneously with 
rising in tube H has also travelled upwards in siphon G, will 
have reached the top of this siphon, which then commences to 
flow. 

Through the siphon G a much larger quantity of water is 
disposed of than flows in through the cock S, so that the vessel 
K is rapidly emptied again. 

The moment the pressure on this vessel is released the liquid 
from C returns into the lower part of the vessel K and the float 
N to its original position. As soon as the liquid in C has fallen 
below the gas in the outlets to this vessel the whole of the remain- 
ing gas is rapidly sucked out through E by the ejector Q. 



CHAPTER IV. 
CORROSION AND INCRUSTATION. 

THE water supplied to a boiler for forming steam may 
corrode the iron of the boiler, or it may deposit material that 
j can form a scale or incrustation ; both actions may go on at 
the same time. 

Pure water, free from air and carbon dioxide, has little or 
no solvent action on iron, even though some other metal, 
such as copper, which may with the iron form the elements of 
a galvanic couple, be present. On the other hand, iron will 
not rust if placed in an atmosphere of dry air or dry carbon 
dioxide. All natural water, rain-water, water from wells, rivers, 
lakes, or the sea, contains air in solution, and carbon dioxide 
is not infrequently found in such waters. Iron is rapidly 
acted upon by water containing air or carbon dioxide, and, on 
the other hand, iron rusts rapidly in air or carbon dioxide when 
moisture is present. Again, distilled water, as from the sur- 
face condenser of a marine engine containing more or less oil, 
or the substances resulting from the action of steam on oil, 
causes corrosion in boilers that are free from scale. To avoid 
rusting of boilers when not in use they ought to be either 
quite dry inside or they ought to be entirely filled with 
water — preferably water that has been freed from air by boil- 
ing. In the American Navy it has been the custom to dry 
out boilers and paint them inside with mineral oil preparatory 
to laying them up. In the English Navy the boilers are 
dried out, a pan of glowing charcoal is placed in the boiler to 

103 



io4 



S TEA M-B OILERS. 





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CORROSION AND INCRUSTATION. 105 

consume the oxygen of the air, and quicklime is introduced 
to absorb moisture. 

Mineral Impurities. — The impurities found in water sup- 
plied to land boilers are commonly carbonate of lime and 
sulphate of lime, with more or less organic matter, and some- 
times sand or clay held in suspension. The table on page 104 
gives the number of grains of various mineral substances held 
in solution in water from several sources. 

Water supplied to land boilers is either hard or soft ; the 
first contains appreciable quantities of lime, and the other 
usually contains little solid matter of any sort. The first three 
examples in the table on the preceding page may be taken as 
typical soft waters, and all the others, except the last two, as 
typical hard waters. While there is considerable difference 
in the amounts and the composition of the solids in solution 
in the several examples of hard water, it will be seen that 
they are all characterized by a considerable amount of calcium 
and magnesium carbonates, and (with the exception of Nos. 6 
and 9) accompanied by a comparatively small amount of cal- 
cium and magnesium sulphates. It will be noticed that Mis- 
souri River water is distinctly worse than Mississippi" River 
water, not only in that it contains more of the carbonates, 
but because it contains a considerable quantity of sulphates. 
No. 9, from a well at Downer's Grove on the C, B. and Q. 
R. R., a few miles from Chicago, has been selected as an 
example of a very bad hard water, especially as it contains so 
much sulphate. The reason for considering the sulphates of 
lime and magnesia so deleterious will appear a little later. 
Note will be made that the water from the Mississippi River 
at two different places, and presumably at different seasons of 
the year, vary considerably, especially in the amount of mat- 
ter held in suspension. 

In some places in the western parts of the United States 
the only available waters for making steam are strongly im- 
pregnated with alkalies and borax. Such waters have so 



1 06 S TEA M- BOILERS. 

deleterious an action on boilers that the advisability of using 
a surface condenser, as at sea, the distillation of water by a 
multiple-effect evaporator, or the introduction of a supply of 
good water even from remote places, is worthy of considera- 
tion. If the use of such water cannot be avoided, a competent 
chemist should be consulted to suggest methods for ameliorat- 
ing the bad effects so far as possible. As each case is liable 
to require special treatment, no further discussion appears 
profitable in this place. 

The carbonates of lime and magnesia are held in solution 
in water by an excess of carbon dioxide and are completely 
precipitated by boiling. They are thrown down from water 
supplied to a boiler, in the form of a white or grayish mud, 
provided there are not other impurities that cement them to 
gether and form a hard scale. The customary and sufficient 
method of treating boilers supplied with water containing car- 
bonates of lime and magnesia is to let the boiler, while full, 
cool down, and then run out the water and thoroughly wash 
out the boiler with a strong stream from a hose. If the water 
is blown out under steam-pressure the deposits are hardened 
and are removed with difficulty. While pure carbonates are 
easily treated as just described, the presence of other impu- 
rities, such as oil or organic matter, or of sulphate of lime, is 
likely to make the deposits hard and adhering. 

Sulphate of lime is much more soluble in cold than in hot 
water, and is entirely thrown down from water at a tempera- 
ture of 280 F., corresponding to 35 pounds pressure of steam 
above the atmosphere. It forms a hard and adhering scale, 
and even in comparatively small quantities has a bad effect on 
scales and deposits composed of carbonates, as has already 
been suggested. The bad effect of deposits from water con- 
taining calcium sulphate is much ameliorated by introducing 
carbonate of soda or soda-ash into the boiler with the feed- 
water. The result is to give a deposit of calcium carbonate 
in the form of a fine white powder, which must be washed 



CORROSION AND INCRUSTATION. 107 

or swept out, and sodium sulphate in solution, which must be 
blown out from time to time. 

If the mineral matters in the water are known from a 
chemical analysis, the quantity of carbonate of soda to be used 
may be calculated as follows: 

Example. — Find the weight of carbonate of soda required 
per day for a boiler supplied with 1000 gallons of water per 
day from the well at Downer's Grove. 

From the table on page 104 it appears that each gallon of 
the water contains 14.037 grains of CaS0 4 and 25.422 grains 
of MgS0 4 . The formula for soda crystals being Na 2 C0 3 -f- 
ioH 2 0, the reactions, neglecting the water of crystallization, 
will be 

CaS0 4 + Na 2 CO s = CaC0 3 + Na 2 S0 4 ; 
MgS0 4 + Na 2 C0 3 = MgCO s + Na a S0 4 . 

If x x is the grains of carbonate of soda to act on the cal- 
cium, we have 

CaS0 4 ;Na,C0 3 + ioH 2 = 14.037 :*»; 
404-32 -t- 4 X 16 : 2 X 23 + 12 + 3 X 16 + 10(24 l6 ) 

= 14.037:*,. 
.*. x x = 29.52 grains. 

The magnesium sulphate which is soluble is also changed 
into the carbonate and thrown down as a white precipitate, 
adding to the deposit. The number of grains of carbonate 
oi soda required for this reaction is found as follows : 

MgS0 4 :Na 2 C0 3 4 ioH 2 = 25.422:*,; 
244 32 44X16:2 X 23 4 1243 X 164 10(2 416) 
= 25.422 : *,. 
.*. x^= 60.59 grains. 

The total weight of carbonate of soda per gallon is therefore 
29.52+60.59= 904, 



io 8 STEAM-BOILERS. 

and the weight required for iooo gallons is 

90 X 1000 , , 

= 12.9 pounds per day. 

7000 

It is advisable that soda, or any other chemical for acting 
on the impurities of feed-water, shall be introduced at regular 
intervals. Sometimes a weight, or measured portion, is thrown 
into the feed-water in a tank or reservoir, from which it is 
pumped. Sometimes the chemical, dissolved in water or 
diluted with water, is placed in a small tank or receptacle that 
may be temporarily connected with the suction of the feed- 
pump. If this method is used care must be taken not to 
admit air to the pump and so derange its action. 

Soda-ash is commonly used instead of carbonate of soda, 
as it is cheaper and somewhat more efficient, on account of the 
caustic soda it may contain. Its chemical composition is 
uncertain, and it is therefore impossible to make satisfactory 
calculations for the quantity to be used. This, however, is 
commonly no real objection, for we seldom have a chemical 
analysis of the water, and cannot determine directly how much 
soda is required. 

An excess of soda in a boiler is liable to cause foaming, 
and at high temperatures, corresponding to pressures now ha- 
bitual for steam-boilers, the soda is apt to attack the inside of 
water-glasses ; any indication of either action should raise the 
question whether too much soda is used, but the absence of 
such an indication does not show that we are using the right 
quantity. When a hard scale is formed by a water known to 
contain lime, we may infer that sulphates are present, and may 
find by trial the amount of soda to be used. Unfortunately 
other impurities, such as organic matter, cause the formation 
of hard scale, and make this method uncertain. Such impur- 
ities often produce discoloration, and thus betray their pres- 
ence. The deposits of lime, whether carbonates or sulphates. 
are commonly white or grayish, or sometimes fawn color. 



CORROSION AND INCRUSTATION. 109 

It is sometimes proposed to use ammonium chloride, or 
sal-ammoniac, to break up lime compounds; in the first 
place, only the carbonates are acted upon by this reagent, 
and in the second place, the reagent itself, or the resultant 
chlorides, are liable to be broken up, giving free chlorine, 
which attacks the boiler. 

Tannic acid, either commercial acid or in the crude state, 
may be used to break up a scale already formed ; but as 
tannic acid does not decompose the sulphates , and as the 
compound of the acid with lime is not soluble, its use appears 
to be restricted. Many proprietary boiler compounds depend 
on tannic acid for their action. Acetic acid may also be 
used to break up the carbonates, but it likewise has no action 
on the sulphates ; the carbonates are changed into soluble 
acetates, and can be blown out. Both tannic acid and acetic 
acid attack iron, but are not so dangerous as sulphuric or 
hydrochloric acids, which are sometimes recommended for 
breaking up scale. When a scale is once formed the safer 
way is to remove it with proper chipping and scaling tools ; 
but this will be found to be impossible for many types of 
boilers unless they are largely dismembered for that purpose. 

When river-water is used in boilers, various earthy im- 
purities are liable to be carried into boilers, such as clay and 
sand, together with soluble matters. Even waters from 
ponds or wells may contain considerable matter in suspension. 
Such substances can sometimes be removed by filtering or by 
allowing the water to stand so that the insoluble matter may 
be deposited. Very commonly a systematic blowing out 
from the surface of the water and the bottom of the boiler 
will remove such impurities from the boiler. If, however, 
lime and magnesium carbonates and sulphates are present, 
suspended matter is carried into the scale, and the scale may 
be made more troublesome in consequence. The carbonates 
are more likely to form a hard scale if any binding material- 
such as clay, is present. 



no 



S TEA M-B OILERS. 



Fig. 36 shows the section of a feed-pipe which was nearly- 
choked with scale from lime-water. Though the deposit of 
scale in a horizontal piece of feed-pipe where the water may 
be heated by conduction and otherwise, especially during 
intervals of feeding, is probably more rapid than in the boiler 
itself, this may serve to call attention to the extent to which 
scaling may occur when precautions are not taken. 




Fig. 36 * 

Lime-extracting Feed-water Heater. — It has been 
pointed out that carbonate of lime can be completely pre- 
cipitated by boiling to drive off the excess of carbonic acid ; 
carbonate of magnesia if present is thrown down at the same 
time. Also sulphate of lime is thrown down at 280 F., cor- 
responding to 35 pounds pressure above the atmosphere. 
It is evident that lime compounds can be removed from feed- 
water by heating it and removing the precipitated lime before 
feeding it to the boiler. For this purpose we may use a 
heater such as the Hoppes heater and purifier shown by Fig. 
37, which consists essentially of a series of cylindrical pans 

* This figure and Figs. 40 to 43 were kindly loaned by the Hartford Steam 
Boiler Inspection and Insurance Co. 



CORROSION AND INCRUSTATION. 



Ill 



of sheet steel, 1,2, 3, 4, 5, and 6. The feed-water is pumped 
into the upper pan, from which it overflows, and, trickling 
along the bottom, it drops into the pan 2. From 2 the 
water overflows into 3, and so on. 

The capacity of the heater depends on the number of 
sets of pans, which varies from one to four. The pans are 
enclosed in a steel shell, from which one end may be removed 
for cleaning the pans. Feed-water is pumped in at B\ steam 
from the boiler is admitted at A ; the feed-water after being 
heated and purified runs out at D on the way to the boiler; 




Fig. 37. 

at C there is a blow-out, from which air and gases may be 
blown out when the heater is started, or at other times. 

It is desirable that the pipe D shall drop down below the 
water-level in the boiler before any turns or horizontal pipes 
are attached. The water runs from the heater to the boiler 
by gravity only, and the heater must be placed high enough 
for this purpose. It is also desirable that the feed-pump be 
supplied with steam from the heater so as to continually 
remove the carbonic acid, air, or other gases given off from 
the feed-water. 



112 



S TEA M-BOILERS. 



The feed-water as it trickles along the under sides of the 
pans in a thin film is heated by the steam, and the lime com- 
pounds are deposited in form of a scale or incrustation, 
Meanwhile mud, sand, and other mechanical impurities settle 
to the bottom of the pans. 

After the heater has been at work a month or so, depend- 
ing on the amount of lime in the water, the pans must be 
removed and cleaned. The steam-pipe and the pipe leading 
to the boiler are shut off by proper valves, and cold water is 
pumped in and allowed to run to waste at the blow-off. The 
contraction of the pans cracks off hard scale and makes it 
easier to remove. When the heater is first opened the scale 
is usually soft and can be readily removed ; it is liable to 
harden when exposed to the air and allowed to dry. 

A heater for use with exhaust-steam, by the same makers, 
differs from this mainly in that there is a device for extract- 
ing oil from the steam before it meets the feed-water, and in 
that it is run at atmospheric pressure. Such a heater will not 
remove sulphate of lime ; and further, since it is difficult if 
not impossible to remove oil from exhaust-steam, it is proba- 
ble that some oil will be carried over into. the boiler. 

Sea-water. — The following table gives an analysis of sea- 
water by Professor Lewes of the Royal Naval College, to- 
gether with an analysis by him of a typical boiler deposit from 
a marine boiler: 

SALTS IN SEA-WATER AND COMPOSITION OF MARINE- 
BOILER SCALE.* 



Calcium carbonate (chalk).. 
Calcium sulphate (gypsum). 

Magnesium sulphate 

Magnesium chloride 

Magnesium hydrate 

Sodium chloride (salt). .... 

Silicia (sandy matter) 

Moisture 



Sea-water. 
Grains per Im 
perial Gallon. 



3-9 

93-1 

124.8 

220.5 

1850.I 



Marine-boiler 

Scale. 

Per Cent. 



O.97 

85.53 



3-39 
2.79 
I.I 

5-9 



* Trans. Inst. Naval Arch., vol. xxx. p. 330. 



CORROSION AND INCRUSTATION. 113 

The three principal constituents of the marine scale are cal- 
cium sulphate, calcium carbonate, and magnesium hydrate, 
of which the first forms the greater part of the scale. 

The calcium carbonate is kept in solution by the carbonic 
acid in the sea- water, just as is the case for fresh water con- 
taining carbonate of lime, and is deposited when the carbonic 
acid is driven off by heat. There is, however, a reaction 
between the calcium carbonate and magnesium chloride at the 
temperature and pressure in the boiler, giving a deposit of 
magnesium hydrate and leaving calcium chloride in solution, 
so that only part of the calcium carbonate appears in the scale ; 
and on the other hand, we may thus account for the presence 
of the magnesium hydrate in the scale. 

The calcium sulphate forms so large a part of the scale, that 
we will give attention to it only in the further discussion. Cal- 
cium sulphate is more soluble in water at 95 ° F. than at any 
temperature higher or lower; and the solubility decreases with 
the rise of temperature, till at about 280 F., which corre- 
sponds to 50 pounds pressure absolute to the square inch, or 
35 pounds above the atmosphere, the entire amount of cal- 
cium sulphate is deposited. In the early history of the marine 
engine, when low pressures of steam prevailed, we find jet con- 
densers in use, and the boilers, which were fed from the brine 
in the hot-well, were kept fairly free from scale by blowing 
out the concentrated brine. It was then customary to supply 
half again as much feed-water as was evaporated, the excess 
being compensated by the concentrated brine blown out, and 
the water in the boiler had three times the degree of concen- 
tration found in the sea. As high-pressure steam came into 
use, surface condensers became indispensable. When surface 
condensers first came into use the waste of steam from leakage 
and otherwise was made up from water taken from the sea, 
with the result that the boilers gradually accumulated a heavy, 
dense scale. Since it is customary to have an auxiliary boiler, 
called a donkey-boiler, on steamships, the first device to avoid 
the scaling from the use of sea-water in the main boilers appears 



H4 



STEAM-BOILERS. 



to have been to supply the loss of steam from the donkey- 
boiler, which was fed from the sea. This of course only trans- 
ferred the difficulty from one place to another, even though a 
less objectionable one. At present the loss is made up by 
vaporizing sea-water in a special boiler, which is heated by 
steam-coils supplied with steam from the main boilers. The 
pressure may be low enough in this vaporizer to avoid the 
total precipitation of the calcium sulphate, and the brine may 
be kept at any desirable degree of saturation by blowing out, 
as in the early marine practice ; and further, the vaporizer is 
so made that the steam-coils may be readily cleared from 
scale. 

It should be pointed out that the decomposition of the 
calcium sulphate in sea-water by the aid of soda is impracti- 
cable, on account of the large quantity of magnesium carbonate 
thrown down by reaction on the magnesium sulphate. 

A boiler fed with water condensed in a surface condenser, 
as is now common in marine practice, is liable to two diffi- 
culties : (i) the distilled water is apt to corrode or pit the plates 
of the boiler, and (2) the cylinder-oil used in the engine is 
liable to be carried over into the boiler and form oily scales 
and deposits. 

When sea-water is used in the boiler, either as the main 
boiler-feed or merely to supply the waste, the boiler-plates are 
protected by the scale of calcium sulphate, and general corro- 
sion or local pitting is seldom troublesome. When care is 
taken to avoid the use of salt water, supplying the waste with 
fresh water from a distiller or otherwise, general corrosion and 
local pitting have both been found to occur to a dangerous 
degree. A simple remedy appears to be to form a very thin 
scale by the use of sea-water, and then avoid further use of 
sea-water. It is, however, found that water from a surface 
condenser will gradually dissolve off such a scale, and it must 
be occasionally renewed. There is also an objection to the 
introduction of any lime compound into a boiler, as wili appear 



CORROSION AND INCRUSTATION. 115 

in the discussion of the difficulty from the collection of oil in the 
boiler. In both the United States and the English navies it is 
customary to use slabs of zinc to protect the boiler-plates from 
corrosion. The zinc is fastened to or hung from the boiler- 
stays, with which metallic connection should be made to in- 
sure galvanic action. The zinc is gradually consumed, and 
becomes soft and friable, so that the slabs require renewal. 
It is recommended to supply 1/4 of a pound of zinc for each 
square foot of grate-surface. 

It is a familiar fact that the cylinders of an engine may be 
oiled by introducing the oil into the supply-pipe, and that the 
oil will be carried quite thoroughly over the surface of the 
cylinder by the steam ; and, further, that the oil is carried out 
of the cylinder by the steam, and will appear in the condensed 
water in the hot-well. It is evident that any oil is liable to 
be injurious if it gets into a boiler. It is, consequently, cus- 
tomary to filter the water from a surface-condenser, to remove 
the oil as far as possible. For this purpose sponges have 
been used in the navy; they, of course, must be occasionally 
taken out and washed free from oil. A very simple and effi- 
cient filter has been made in the form of a rectangular box, 
with perforated plates near the ends ; the water from the hot- 
well runs into one end compartment, passes through a mass of 
hay in the middle compartment, and is drawn from the further 
end compartment by the feed-pump. When the hay becomes 
foul it is thrown away, and fresh hay is put in. Professor 
Lewes advises for a filter a long tube filled with charcoal 
about the size of a walnut ; of course the charcoal should be 
renewed when necessary. It cannot be expected that any 
system of filtering will remove all the oil from the water, but 
the larger part may be removed. It is advisable that no more 
oil than necessary shall be used in the cylinders of the engine. 

Professor Lewes* gives the following account of an inves- 

* Trans. Inst. Nav. Arch., xxxu. page 67. 



1 1 6 S TEA M-B OILERS. 

ligation of the collapse of the furnace-flues of a large Atlantic 
steamer, which made the voyage in twelve days : 

The boilers were five and a half years old, and were refilled 
with fresh water at the end of each voyage, while the waste of 
the voyage was made up by the use of about 70 tons of fresh 
water, but during the last voyage sea-water was used for this 
purpose. Every four hours, while under steam, four pounds 
of soda crystals were put in the hot-well, making two hundred- 
weight during the run, the total capacity of the boilers being 
81 tons. For lubricating purposes seven pints of valvoline 
were used in the cylinders every four hours. 

When in port the boilers were allowed to cool down, and 
the water was run off and they were swept down with stiff 
brushes, and were afterwards sluiced out with a hose shortly 
before being filled with fresh water. No trouble occurred 
until five voyages before the final collapse, when some of the 
furnaces began to creep in : they were stiffened with rings and 
stays; and on succeeding voyages the whole of the furnaces 
got out of shape one after the other. Examination showed 
that they had never been very heavily scaled. On the furnace- 
crown there was only a slight white scale not more than 1/64 
of an inch thick, while on the bottom of the furnaces there was 
a brown oily deposit 1/16 of an inch thick, which in other 
parts of the boiler increased to 1/8 or 3/16 of an inch. 

The valvoline was a pure mineral oil with a specific gravity 
of 0.889 an d a boiling-point of 37 1 ° C. 

The composition of scales from several parts of the boiler 
is shown in the table on the next page. 

Careful examination of the organic matter and oil in these 
deposits showed that half of it was valvoline in an unchanged 
condition, which had collected around small particles of calcic 
sulphate. 

All the deposits were rich in oily matter except the top 
of the furnaces, i.e., the place where the collapse occurred. 
There the scale was not only nearly free from oil, but per- 
fectly harmless both in quantity and quality. It appeared 



CORROSION AND INCRUSTATION. 



II 7 



COMPOSITION OF DEPOSITS IN A MARINE BOILER. 



Calcium sulphate 

Calcium carbonate 
Magnesium hydrate . . . 
Iron, alumina, siiica. . . 
Organic matter and oil 

Moisture 

Alkalies 



Q.4I 



B v 
S3 

o S 

02 3 



84.87 
5-90 
2.83 

2-37 

3-23 
0.80 



59-n 
6.07 

11.29 
2.85 

19-54 
1. 14 



09 


V 




XI 


> 


a 


3 




x e 

rt 5 • 
»j w w 



"Z a u 







■55 S« 


73 


O <s 3 


offlffl 


c/) 


P 


Q 


50.92 


II.60 


22.52 


4.18 


O.82 




14.12 


22.21 


7.09 


7-47 


9-14 


34-85 


21.06 


50.20 


27-95 


1. 17 


4- 23 


5-79 


1.08 


1.80 


1.80 



entirely improbable that the scale on the top of the furnaces 
could be in its original condition. 

When oil has entered a boiler the minute globules, if in 
large quantity, coalesce to form an oily scum on the surface, 
or if in small quantity remain in separate drops, but show no 
tendency to sink on account of their low specific gravity. 
They, however, come in contact with solid particles of calcium 
sulphate, coat them with oil, and so the light oil becomes 
loaded till it is easily carried along by convection-currents and 
adheres to surfaces with which it comes in contact, which 
are quite as likely to be the under surfaces of tubes as the 
upper surfaces. Since some brine is liable to find its way to 
the boiler, from leakage into the condenser or otherwise, even 
when sea-water is not used directly, this action will occur in 
a boiler supposed to contain fresh water only. 

The deposits thus formed are very poor conductors of heat, 
and the oily surface interferes with contact with water. On 
the crown of the furnace this soon leads to overheating of the 
plates, and the deposit begins to decompose, the lower layer 
in contact with the plate giving off gases which blow up the 
greasy layer, ordinarily only 1/64 of an inch thick, to a spongy 
mass 1/8 of an inch thick, which, because of its porosity, is even 
a better non-conductor of heat than before, and the plate be- 
comes heated to redness and collapses. During the last stages 



Ii8 STEAM-BOILERS. 

of this overheating the temperature has risen to such a point 
that the organic matter, oil, etc., in the deposit burns away, 
or is distilled off, leaving behind, as an apparently harmless 
deposit, the solid particles round which it had originally formed. 

Such a deposit is more likely to be produced in boilers 
containing fresh or distilled water, as the low density of the 
liquid enables the oily matter to settle more quickly, while 
with a strongly saline solution it is very doubtful if this sink- 
ing-point would ever be reached ; it is evident also that when 
oil has found its way into the boiler and is causing a greasy 
scum on the surface the most fatal thing that can be done is 
to blow off the boilers without first using the scum-cocks, be- 
cause as the water sinks the scum clings to the tops of the fur- 
naces and other surfaces with which it comes in contact, and 
on again filling up with fresh water it still remains there, 
causing rapid collapse. A very remarkable instance of this 
is to be found in the case of a large vessel in the Eastern trade, 
in the boiler of which an oil-scum had formed. The ship 
having to stop some days in Gibraltar, the engineer took the 
opportunity of blowing out his boiler and refilling with fresh 
water, with the result that before he had been ten hours under 
steam the whole of the furnaces had collapsed. Under some 
conditions the oil-coated particles coalesce and form a sort of 
floating pancake, which, sinking, forms a patch on the crown 
of the furnace at one particular spot, and under these condi- 
tions the general result is the formation of a pocket. 

A curious fact is that these oily deposits are found to con- 
tain a considerable amount of copper. Even mineral oils have 
a solvent action on copper and its alloys, and it is evident 
that the copper in the oily deposits has been obtained from 
the fittings of the cylinder and condenser. Fortunately this 
copper is protected by oil, otherwise serious galvanic mischief 
would result. 

Professor Lewes found from experiment that a coating, 1/16 
of an inch thick, of the oily deposit found in the bottom of a 



CORROSION AND INCRUSTATION. 1 1 9 

boiler, applied to the inside of a clean iron vessel, very greatly 
retarded the transmission of heat from a Bunsen flame, as 
shown by the time required to heat a known quantity of water 
to boiling-point. Using an atmospheric blowpipe, he succeeded 
in raising the outside surface of the vessel, when coated with 
1/16 of an inch of the deposit, to the temperature of the melt- 
ing-point of zinc, and with an oxy-coal-gas flame he fused a 
hole in the bottom of a thin wrought-iron vessel thus coated 
and filled with water. 

He further says that cylinders should be sparingly lubri- 
cated with a pure mineral oil having a high boiling-point, and 
that animal or vegetable oil should never be used, because 
they are decomposed by the action of high-pressure steam, 
producing fatty acids that attack iron, copper, and copper 
alloys. 

Professor Lewes has proposed that marine boilers at sea 
shall have the water supplied with brine from which the lime 
compounds have been precipitated in a closed receptacle by the 
combined action of heat and carbonate of soda. The resulting 
brine contains mainly sodium and magnesium chlorides and 
magnesium sulphate, which do not form scale even though the 
concentration is carried to a higher degree than would occur 
from the supply of the waste of the boiler in this way for a 
voyage of some length. This method has not as yet been 
adopted in practice. Attention is called to the fact that an 
excess of soda should be avoided, since it would cause a bulky 
deposit from the action on the magnesium sulphate brought in 
by leakage of sea- water into the condenser. A description of 
the apparatus for producing this brine without lime salts is 
given in the lt Transactions of the Institution of Naval Archi- 
tects" (Vol. XXX, page 330). 

Organic Impurities. — Water for feeding boilers, unless 
taken from a contaminated source, seldom contains much 
organic matter. Surface water from rivers or ponds may con- 
tain some vegetable matter, but if there are no other impuri- 



120 



S TEA M-B OILERS. 



ties such organic matter will not cause much trouble unless it 
is allowed to accumulate. The vegetable and other organic 
impurities commonly float on the surface of the water when 
the boiler is making steam, or are carried around by convec- 
tion-currents, and may be blown out through a surface blow- 
out, shown by Fig. 38, It consists essentially of a flattened 




Fig. 38. 
bell or cone of sheet metal extending across the boiler at the 
water-level, and turned so that the convection-currents will 
carry and lodge floating substances in the mouth of the bell. 
The valve in the pipe leading from this bell may be opened 
from time to time to blow out the substances collected in it. 

When a boiler has been at rest for some time, overnight 
for example, the various solids in the boiler, if heavy enough, 
will settle to the bottom, and may be advantageously blown 
out before starting the boiler into action again. This may be 
accomplished by opening the blow-out valve or cock for a short 
time, until the water-level falls a few inches. 

Water from bogs frequently contains vegetable acids that 
are likely to corrode the plates of the boiler: in such cases 



CORROSION AND INCRUSTATION. 



121 



carbonate of soda may be used to neutralize the acids; the 
proper amount must be found by trial. 

The oil used in the engine is liable to get into the ooiier 
if surface-condensing is made use of; this subject has already 
received attention in connection with the discussion of marine- 
boiler incrustations. Surface condensers are not commonly 
used in land practice, except with turbines. The exhaust-steam 
from non-condensing engines is used for heating in radiating- 
, coils, and there is an apparent gain from the use of the warm 




Fig. 39. 



water from the return-pipes. This water is, however, liable 
to be contaminated by oil, and the oil when it gets into the boiler 
may cause serious damage, such as was found to occur in marine 
boilers. If the feed-water has a little vegetable matter in it, the 
effect of the oil is much worse than if the water-supply is pure. 
Again, the oil is very troublesome if the water contains lime 
salts. The bad effect of oil or other impurities on lime-scale 
has been already noted. Usually it will be found better to 
1 eject the water returned from a heating system supplied with 
exhaust-steam, as the apparent economy is liable to be 
more than counterbalanced by damage to the boiler. The 



122 S TEA M-B OILERS. 

externally-fired tubular boilers commonly used in this part of 
the country are liable to bulge in the sheets over the furnace, 
as shown in Fig. 39, if oil gets into them. When the plate 
is cut out a hard deposit of oil, commonly mixed with other 
impurities, will be found adhering to the plate; this deposit 
is a very poor conductor of heat, and it causes so much over- 
heating of the plate that it bulges out under the pressure of 
the steam. 

In isolated cases it will be found that water of a stream 
may be so contaminated with chemicals from some industrial 
establishment that it acts energetically on the boiler-plates ; 
in such case the water must be abandoned unless the contam- 
ination can be stopped. 

Kerosene and Petroleum Oils. — Both crude petroleum 
and refined kerosene have been used in steam-boilers to miti- 
gate the effect of incrustations of calcium carbonate and calcium 
sulphate. From what is known of the bad effects of the 
heavier petroleum products, such as the mineral oils used for 
lubricating steam-engine cylinders, it appears to be unwise 
to introduce crude petroleum into a steam-boiler. The same 
objection does not apply to refined kerosene, which is not 
known to have any bad effect in a boiler. Both oils are said 
to change the deposits of lime from a hard scale to a friable 
material, which may be easily removed. It is further said that 
these oils will soften and loosen scale already formed. In one 
case 40 gallons of kerosene were used in 24 hours in the 
boilers of a steamer of about 3000 horse-power. These 
boilers showed no incrustation, but considerable corrosion. 

Corrosion is distinguished as general corrosion or wasting, 
pitting, and grooving. 

General corrosion is difficult to detect, as it acts more or 
less uniformly over large surfaces, and even at riveted joints 
the two plates and the rivet-heads waste away equally, so that 
the thinning of the plates is not easily noticed. Old boilers 
not infrequently fail from general corrosion, and then are 



CORROSION AND INCRUSTATION. 1 23 

likely to fail in the plate rather than in the riveted joint, where 
the double thickness of plate gives an advantage. Boilers 
that have been at work should have the plates below the water- 
line drilled and the thickness measured ; if the effective thick- 
ness of the plate is found to be much reduced, the working 
pressure should be made proportionately lower. Fig. 40 




Fig. 40. 

shows an example of general corrosion, and Fig. 41 another, 
but complicated with cracking at the rivet-holes. Both show 
the protection given to the plate by the rivet-heads, and one 
may readily see how the wasting of the rivet-heads "may be 
overlooked. 

Pitting is likely to occur when the corrosion takes place 
rapidly. It appears to be due to lack of homogeneity of 
the metal of the plate, and sometimes appears to indicate 
galvanic action. Though every precaution to avoid gal- 
vanic action should be taken, it is better to assume damage 
to be due to such action only when there is direct evi- 
dence of its existence. Fig. 42 shows pitting over a large 
surface, and Fig. 43 shows local pitting in the corner of a 
flanged plate with general corrosion of the flat surface of the 
plate. It is fair to assume that the disturbance of the metal 
in the process of flanging may determine the vertical forms 
of the pitting. The horizontal plate shows irregular pitting. 

Grooving is usually due to the combination of springing 
or buckling of a plate and local corrosion. The buckling may 
be due to insufficient staying; then the plate springs back 
and forth as the steam-pressure varies. Or buckling may be 
due to improper staying or fastenings, which localizes the 



124 



S TEA M-B OILERS. 




CORROSION AND INCRUSTATION. 1 25 

change of shape due to expansion. In either case the metal 
is fretted at the place where the greatest bending takes place, 
and very much weakened. A crack is liable to be formed, 
which may grow wider and deeper till the plate shows signs 
of failure. Such cracks may be very narrow and difficult to 
find, but, usually the fretting of the metal, whether a crack is 
formed or not, is accompanied by local corrosion, which 
makes a groove of some width. If the water used forms a 
scale on the boiler-plates, the working of the metal throws 
off the scale and exposes the surface to the water so that cor- 
rosion takes place there, though elsewhere the plate is pro- 
tected. 

As one example of insufficient staying, we may take the 
flattened surface in a wagon-top locomotive-boiler (Plate II), 
where the barrel is expanded to join the shell over the fire- 
box. The surface cannot be stayed from side to side for lack 
of space between the tubes, and is merely stiffened by rivet- 
ing three pieces of T iron to the shell. In this case the T 
irons have through-stays at their upper ends over the tubes. 
Grooving is liable to occur in this locality even when the 
plates are stiffened as shown. 

Grooving from too great rigidity is liable to occur in the 
end-plates of Cornish and Lancashire boilers (see pages 7 and 
8). The long furnace-flues expand more than the external 
shell, and expand more at the top than at the bottom, due to 
the heat of the furnace and of the gases in the flue beyond 
the furnace ; and further, the circulation of water under the 
flues is likely to be imperfect, so that the bottom of the flue 
is not so hot as the top. These unequal expansions must be 
accommodated by the springing of the end-plates, and if the 
springing is too much localized, grooving is sure to occur. 
The furnace-flues should be at least nine inches from the 
shell, and the end-plates should be flanged where they are 
joined to the flues and shell, instead of using angle-irons. 
The use of gusset-plates for staying the ends of these boilers 



126 STEAM-BOILERS. 

is likely to give too much rigidity and to localize the spring- 
ing of the plates, unless care is taken to avoid it. 

Grooving from either too great or too little rigidity can be 
avoided only by a proper design, which must be guided by 
experience. If a boiler shows defects of staying, it may be 
possible to put in additional stays after the boiler is com- 
pleted and at work; or in some cases too great rigidity may 
be remedied by rearranging the staying. Such remodelling of 
a boiler is usually difficult and unsatisfactory. 

Prevention of Corrosion. — The oxygen in the air which is 
present in water is one of the main causes of general corrosion 
in boilers. About 5 per cent of air by volume is present in 
water which has not been heated. This air being driven off by 
heat leaves the oxygen free to attack the plates of the boiler. 
In some plants where the corrosion has been serious it has been 
found advisable to prevent the oxygen liberated from the feed- 
water from getting into the boiler. This is accomplished by 
passing the heated feed-water through a closed chamber rilled 
with iron or steel turnings or chips, which, by becoming oxidized, 
use up the oxygen. These turnings have to be renewed at fre- 
quent intervals. 

Loss from Blowing Out Brine. — In the discussion of the use 
of sea-water in marine boilers, reference was made to the custom 
of feeding one-and-a-half times as much water as was evaporated. 
The feed-water was taken from the hot- well of the jet condenser, 
and was nearly as salt as sea- water, which contains about 1/32 
of its weight of salt. The one-half excess of water fed was 
blown out, and carried with it all the salt of the entire feed- 
water; it consequently contained 3/32 of its weight of salt, and 
the brine in the boiler had the same degree of concentration. 

In calculating the loss from blowing out hot brine it is cus- 
tomary to assume that the specific heat of sea-water and also 
of the hot brine is the same as that of fresh water; accuracy in 
this calculation is not essential. 

For example, find the loss from blowing out hot brine to 



CORROSION AND INCRUSTATION. 1 27 

maintain the concentration in the boiler at 3/32, when the 
boiler-pressure is 30 pounds by the gauge and the temperature 
in the hot-well is 140 F. 

The absolute pressure corresponding to 30 pounds by the 
gauge is 44.7, found by adding the pressure of the atmosphere. 
Since no refinement is needed in this calculation we will use 
instead 45 pounds absolute. A table of the properties of satu- 
rated steam (see Appendix) gives for the heat of the liquid at 
45 pounds absolute, 243.7 thermal units; this is the heat re- 
quired to raise one pound of water from 32 F. to 2 74°.5 F., 
that is, to the temperature of steam at the pressure of 45 pounds. 
The same table gives for the heat required to vaporize one 
pound of steam from water at 274^5 against a pressure of 45 
pounds, 927.5 thermal units. But it is assumed that the feed- 
water has a temperature of 140 F. when taken from the hot- 
well; the corresponding heat of the liquid is 108.0 thermal units. 
Consequently, to raise a pound of water from 140 F. and 
vaporize it under the pressure of 45 pounds will require 

9275 -f- 243.7 ~~ 108.0 = 1063.2 

thermal units. This is the heat usefully employed. 

Meanwhile for each pound of water vaporized half a pound 
of water is heated from 140 F. to 274°.5 F., and then thrown 
away. The heat required to raise half a pound of water from 
140 F. to 274°.5 F. is 

1(243-7 ~ 108.0) = 67.8 

thermal units. This is the heat wasted. 

The total heat applied to forming steam and heating the 
brine blown out is 

1063.2 + 67.8 = 1131.0. 
The per cent of heat wasted is consequently 

67.8 
100 X — ' — = 6 per cent. 
1131.0 



128 STEAM-BOILERS. 

A considerable portion of the heat lost in the hot brine may 
be transferred to the feed-water drawn from the hot-well by 
the aid of a feed-water heater, and thus saved. A simple form 
of heater may be made by carrying the hot brine through a 
small pipe inside the feed-pipe; the currents of water will 
naturally flow in opposite directions, and thus give the most 
efficient interchange of heat. If the hot-well is near the boiler 
the feed-pipe may not be long enough to allow of this form of 
heater. 

The density of brine in the boiler is ascertained by a sali- 
meter, which is a form of hydrometer graduated to read zero in 
fresh water, 1/32 in sea-water, and the graduation is extended 
to give the density of brine in thirty seconds, so far as may be 
needed. When jet condensers were used at sea it was cus- 
tomary to carry the density to 3/32 only. With surface con- 
densers the density is frequently carried as high as 6/32; no 
inconvenience is found in this custom, and as less water is taken 
from the sea the formation of incrustation is less rapid. 



CHAPTER V. 

SETTINGS, FURNACES, CHIMNEYS, MECHANICAL STOKERS, 
ECONOMIZERS, AND INDUCED DRAUGHT FANS. 

The Boiler-setting" for a stationary boiler consists of the 
foundation and so much of the flues and furnace as are ex- 
ternal to the boiler proper. The entire furnace of externally- 
fired boilers is in the setting, and in some cases, as with the 
plain cylindrical boiler, the flues are also formed by the set- 
ting. Some internally-fired boilers — for example, the Lanca- 
shire boiler — have flues in the setting in addition to the boiler- 
flues; others, like the upright boiler (Fig. 6, page n), have 
only a foundation. Locomotive-boilers rest on the frame of 
the locomotive ; they can scarcely be considered to have any 
setting. Marine boilers are seated on plates that are built 
into the framing of the ship. 

Foundations. — The kind of foundation needed depends upon 
the type of boiler to be set and upon the land. With boilers 
of the horizontal multitubular type the weight is distributed by 
the brickwork of the side walls over a considerable length of the 
foundation. With many of the water-tube boilers the load is 
brought to the four corners of the setting. 

On good land a floated concrete bed 2 feet thick extending 
1 foot all around outside of the setting is usually sufficient. 

On made land piling is often necessary. The piles should 
be cut off below water and a concrete footing made over the 
piles. 

The safe bearing loads carried by different kinds of soil are 
generally taken as follows: 



i3o 



STEAM-BOILERS. 



Good solid natural earth 4 tons per square foot. 

Gravel, well packed and confined, 8 tons per square foot. 

Dry sand, well packed and confined, 4 tons per square foot. 

Dry sand not confined, 2 tons per square foot. 

Marshy soils and quicksands, 1/2 ton per square foot. 

Soft wet clay, 1 ton per square foot. 

Thick beds of clay, 4 tons per square foot. 



I ' 1 ' 1 ' ■ PT FIRE BRICK 



HARD BRICK 




Fig. 44 



Concrete for footings may be mixed in the following pro- 
portions: Four bags of Portland cement, three barrows or 
barrels of a clean sharp sand, and five barrows of crushed stone. 
At the end of two weeks this will have set sufficiently hard for 
the work of erecting the boiler to be begun. 

Cylindrical Tubular Boiler-setting.— The setting for a 
pair of cylindrical tubular boilers, like the boiler represented 
on Plate I, is shown by Figs. 44 and 45. The foundation for 
the boiler-setting is a solid bed of concrete 17 feet 8 inches wide, 



SETTINGS. 



!3 X 



and 21 feet 8 inches long, and 24 inches thick. On firm soil 
the foundation may be conveniently made of large rough-stone 



t 



-21-8- 




00 ?12* 



-24- 



_ 



-»*>rl?~<— 24~ » 






Q 



© 



® 










© 



=r 



m 



1 



-19-8- 




^' : - '--:,. CONCRETE *.,_-;V, < 



Fig. 



work, about three feet wide, under the side, middle, and end 
walls only. 



I32 STEAM-BOILERS. 

On this foundation there are built the walls that support 
and enclose the boiler and the furnace. The outer walls at 
the sides and rear are double, with an air-space to check thr 
conduction of heat. The boilers are each supported by two 
brackets at each end; the front brackets rest on iron plates 
which are built into the side walls; the rear brackets have 
iron rollers interposed to allow for expansion. A brick, 
arch is sprung over the boilers to check the radiation of heat. 
The space between the side and end walls over the boilers 
may be filled with sand, for the same purpose. Coal ashes 
are sometimes used, but they are hygroscopic and liable to 
harbor moisture when the boilers are not working, and should 
not be used. Sometimes the tops of boilers are covered with 
brick and buried in sand; or the sand may be used without 
brick. These methods give ready access to the shell for 
inspection or repairs, but are not so good as a brick arch, as 
water can more readily get to the boiler if it should drip from 
leaky valves or fittings. The rear wall is carried a little 
higher than the top row of fire-tubes, then the space is bridged 
over from the side walls by a horizontal mass of brick-work, 
stiffened and supported by T irons. The smoke-box projects 
over the front wall, and has a rectangular uptake on top, lead- 
ing to a wrought-iron flue which carries the smoke to the 
chimney. 

The furnaces under the front ends of the boilers arc 
enclosed by the side walls, the front wall, and a bridge just 
beyond the first ring of the boiler-shell. The grates rest on 
the front wall and the bridge, as shown in vertical section by 
Fig. 45 and indicated in black on Fig. 44. There is a clear 
space of 24 inches between the grate and the boiler, and a clear 
space of 8 inches over the bridge. The top of the bridge is made 
of fire-brick, and all the walls of the furnaces and other spaces 
that are exposed to the fire are lined with fire-brick. The fifth 
or sixth course of fire-brick above the grate should be laid as 
headers, which serve to support the bricks above, while the brick 



SETTINGS. 133 

below the headers are being renewed. All the remainder of the 
brickwork is of hard, well-burned brick. The ash-pit under the 
grate is paved with brick. The floor behind the bridge is covered 
with a layer of sand and paved with brick. 

The side walls are braced by three pairs of buck-staves, with 
through-rods under the paving and over the tops of the boilers. 

The boiler front is cast iron, with doors opening from the 
furnaces and from the ash-pits. There are also doors opening 
from the smoke-boxes to give access to the tubes. Doors through 
the rear wall give access to the space behind the bridge-wall. 

Between the front tube-sheet and wall in front of the boiler 
there should be a distance equal to the length of a tube; for it 
may be necessary in a few months to replace one or more tubes. 
Sometimes when there is insufficient room the boiler is placed 
opposite a door or a window. 

The tubes are cleaned from the front, that is to say, the soot 
is blown from the inside of the tubes by a steam-jet taken in 
through the swinging-doors of the front covering the tubes. 

Any number of boilers of this type can be set side by side in 
battery. 

If it is desired to get as much boiler power as is possible in a 
given space, using this type of boiler, it will be most economical 
to arrange the boilers in two lines with the fronts facing together 
with a distance equal to the length of a tube between the front 
tube-sheets. 

The setting for a two-flue boiler, or for a boiler with several 
large flues in place of the numerous fire-tubes of the tubular 
boiler, is substantially the same as those just described. 

Babcock and Wilcox Water-tube Boiler Setting. — 
This boiler is suspended from a framework built up of I-beams 
with I-beam columns at each corner. The brickwork carries no 
load whatever, the entire load coming to the foundation through 
the columns. 

These boilers may be set with the back wall against the back 
wall of the boiler-house, but it is better to keep at least 3 feet 



134 



STEAM-BOILERS. 



between the two and to bring the gases out through an opening 
in the back wall rather than to take the gases through the space 
between the two drums. 

By referring to Figs. 13 and 14 it is seen that in order to blow 
the soot from the outside of the tubes three openings are needed 
on the side of the setting. On account of this only two boilers 
can be set together, then there must be a space of from 4 to 5 
feet. 

To make it possible to renew a tube in the boiler there should 
be a distance between the bottom hand-hole in the header and the 
wall equal to the length of a tube, the distance being measured 
in a line parallel with the tubes in the boiler. As a matter of 
fact the hand-holes being elliptical it is possible to get a tube 
in even if this distance measures 3 or 4 inches less than that called 
for by the above. 

Stirling Water-tube Boiler Setting. — This boiler is sus- 
pended in practically the same manner as the Babcock & Wilcox. 
Its tubes are cleaned from the side, and access to the drums is 
from the side, so only two of these boilers can be set together. 

Heine Water-tube Boiler Setting. — This boiler is sup- 
ported at the bottom of the water-legs. The front water-leg 
rests on cast iron columns, built into the brickwork and tied 
together by the casting carrying the fire- and ash-pit doors. The 
rear water-leg is supported by brickwork. Between the brick- 
work and the water-leg, plates and rollers are inserted to allow 
the boiler to expand. 

The tubes in this boiler are cleaned of soot by blowing jets 
of steam through the hollow stays which tie the sides of the water- 
legs together. 

There is a stay in the center of the space between four tubes. 
The tubes are blown in this way from the front and from the 
back. 

Any number of boilers may be set side by side, but there 
must be a space at the back of the boiler-setting. 

The hand-hole covers, covering the openings opposite a tube, 



FURNACES. 135 

are round and can only be removed by dropping them down to 
the bottom of the water-leg where a larger hole is left. 

Marine Water-tube Boiler Settings. — Boilers like the 
Babcock & Wilcox, Thornycroft, Yarrow, and Almy are en- 
closed in a sheet-iron casing lined with blocks of non-conducting 
material. Asbestos, or a compound of which magnesia is a prin- 
ciple ingredient, is commonly used. 

Fire-brick and pumice-stone are used with the Thornycroft 
boiler to intercept heat that would be radiated downward. The 
spaces in ships under boilers, being more or less inaccessible, 
and being subject to the influence of heat and moisture, are 
liable to show excessive corrosion. 

Furnaces. — There are certain general conditions to which 
the construction of furnaces should conform if high efficiency 
is desired. Some of these depend on the requirements for 
good combustion, and some depend on the size, strength, and 
endurance of the human frame, since hand-firing is almost 
universal. Some of these conditions are violated in the 
design and arrangement of furnaces in certain types of boilers; 
deviation from them involves either a demand for greater 
strength and skill on the part of the fireman, or a loss of effi- 
ciency, or both. 

These conditions, with examples of good and bad practice, 
are as follows : 

There should be an abundant and uniform supply of air to 
the under surface of the grate. About the only cases where 
this condition is not easily fulfilled is in the design of furnace- 
flues of Lancashire boilers and Scotch marine boilers. 

A small supply of air is required over the grate for burn- 
ing smoky fuels like bituminous coal. This air is very com- 
monly supplied through a circular grid or damper in the fire- 
door. The fire-door is commonly protected from direct radi- 
ation by a perforated wrought-iron plate, which also serves 
to distribute the air coming through this grid. Since the 
air thus supplied is cold, it must be small in amount or 



x ^5 STEAM-BOILERS. 

it will chill the gases and check combustion instead of 
aiding it. 

Leakage of cold air into the furnace, or into the combus- 
tion-chamber or flues beyond the furnace, injures the draught 
and reduces the temperature of the products of combustion, 
and is a direct source of loss. All externally-fired boilers and 
water-tube boilers are liable to suffer from leakage of air. 
Locomotive and Scotch marine boilers are usually free from 
this defect. 

The incandescent fuel on the grate should not come in 
contact with a cold surface. Furnaces lined with fire-brick, 
such as are used for externally-fired boilers, conform to this 
requirement. Vertical boilers, marine boilers, locomotive- 
boilers, and all other boilers having the furnaces in fire-boxes 
or flues, violate this condition, as the plates in contact with the 
fire are kept nearly at the temperature of the water in contact 
with the other side, and are therefore much colder than the 
fire. 

There should be an abundant opportunity for complete 
combustion of gases coming from the fuel with hot air drawn 
through the fuel, before the flame is chilled by contact with 
cold surfaces. This condition is best fulfilled by having a 
clear space over the grate. Externally-fired boilers commonly 
have two feet or more between the grate and the boiler-shell 
immediately over it, and combustion may continue beyond 
the bridge. Locomotive- boilers have from four to six feet 
between the grate and the fire-box crown-sheet, but the flame 
is quickly drawn into and extinguished by the tubes. To aid 
combustion and to protect the lower part of the tube-sheet a 
brick arch is frequently carried across the fire-box, over which 
the flame must pass on the way to the tubes. The lack of 
space over the grate of flue-furnaces, as in the Scotch marine 
boilers, is only partially compensated by the combustion- 
chamber beyond the furnaces. 

Loss from external radiation is almost entirely avoided in 



FURNACES. 137 

internally-fired boilers. Externally-fired boilers are subject 
to more or less loss from conduction and radiation. 

The fire-grate should not be longer nor wider than can be 
conveniently reached by the fireman in throwing on fuel and 
in cleaning the grate. A narrow grate should not be so long 
as a wide grate. In general, a hand-fired grate should not be 
more than six feet long, and if it is over four feet wide two 
fire-doors should be provided. These conditions are usually 
fulfilled by the design of externally-fired boilers, locomotive- 
boilers, and water-tube boilers. Attention has been called 
already to the difficulty of getting proper space for the grates 
in flue-furnaces. With the common diameters of the furnace- 
flues a length of five feet should not be exceeded. Flues in 
marine boilers have been made eight feet long; in such case 
the further end of the grate is sure to be inefficiently fired. 
To aid in firing, and to use the space below and above the 
grate to the best advantage for the supply of air and for 
combustion, the grate is commonly given an inclination down- 
wards of about 3/4 of an inch to the foot. 

As an extreme example of deviation from these propor- 
tions we may cite the Wooten locomotive fire-box, designed 
to burn anthracite slack. The grate is made about eight feet 
wide and twelve feet long. 

For convenience in throwing on coal and in cleaning the 
grates, the floor on which the fireman stands should be about 
two feet below the grate. This can usually be arranged for 
stationary boilers. The grate of a locomotive is commonly 
below the floor of the cab ; this facilitates throwing on the 
coal; some form of rocking grate is used to shake down the 
ashes. The side furnaces of Scotch marine boilers are com- 
monly too high for convenient firing, and the middle furnaces 
may be too low for convenience in cleaning the grate. 

Excessive heat in the fire-room should be avoided as far as 
possible; the labor of feeding and cleaning a furnace for rapid 
combustion is always severe, and when combined with great 



138 



STEAM-BOILERS. 



heat it soon exhausts the fireman. If land boilers are 
properly clothed to avoid radiation, and if the fire-room is 
airy and well ventilated, the heat will not be excessive. It is, 
however, very difficult to avoid excessive heat in the stoke- 
hole of a steamship. Of course the radiation from the glow- 
ing fuel when the fire-doors are open cannot be avoided, but 
it ought to be possible to clothe the fronts of marine boilers 
more perfectly than is now the common practice. Moreover, 
the ventilation of the stoke-hole is commonly defective ; the 
air pours down through the ventilators and makes cold spots 
immediately beneath them, while other parts of the stoke- 
hole are hot. Forced draught with closed stoke hole usually 
gives good ventilation ; with closed ash-pit it is liable to give 
defective ventilation. 

In certain types of water-tube boiler there is not sufficient 
space over the fire to enable the gases to mix. If the unmixed 
gases are chilled by coming in contact with the cold tubes in- 
complete combustion results. Analyses of furnace-gas samples 
taken at different parts of the gas passage often show CO and 
an excess of O. This shows that the gases were not mixed till 
the second or third gas passage was reached, where the tem- 
perature was too low for the CO to burn. 

The Dutch oven-furnace, previously referred to in the dis- 
cussion of independently-fired superheaters, has been applied 
to these boilers and has helped somewhat. By raising the boiler 
up and using the Dutch oven-furnace, as shown by Fig. 46, the 
gases may be made to travel 9 or 10 feet before coming in con- 
tact with the tubes. 

This setting gives very nearly complete combustion and is 
very efficient as a smoke-consuming device. 

A relieving arch in either side wall carries the fire-bricks 
above the arch and makes it possible to renew the fire-brick 
adjacent to the fire without disturbing the bricks above. 

Great care should be taken in laying the fire-bricks in a 
furnace of this sort. The bricks should be laid with as thin a 



FURNACES. 



139 





I 4 STEAM-BOILERS. 

layer of clay between them as will serve to give a uniform bear- 
ing. 

Fire-bricks which have been exposed to the weather during a 
storm or fire-bricks which have been left out in winter weather, 
will crumble as soon as they are heated in a furnace. 

But few masons seem to be aware of this fact. 

Grate-bars are commonly made of cast iron, as it is 
cheaper and lasts as well as wrought iron. Sometimes wrought- 
iron bars are used on locomotives and elsewhere, if they are 
expected to withstand rough usage. 

Cast-iron fire-bars are generally 5/8 to one inch thick at the 
top, and 5/16 to 5/8 of an inch thick at the bottom; they are 
about two inches deep at the ends, and three to five inches deep 
at the middle. To provide for wasting of the upper surface, 
they are made full width for some distance down from the top, 
thus forming a sort of head; then they are rapidly narrowed 
down to a web that is tapered gradually toward the bottom. 
The space between the bars depends on the draught and the 
nature of the fuel; with ordinary coal and natural draught 3/8 
to 1/2 of an inch is allowed. Lugs or projections are cast at the 
ends and at the middle, so that the bars shall be properly spaced 
when laid side by side. With forced draught the bars may be 
3/8 to 9/16 of an inch wide at the top, and the distance between 
the bars may be 1/16 to 1/4 of an inch. The area of the air- 
spaces through the grate-bars is ordinarily from 30 to 50 per 
cent of the area of the grate; if shavings are to be burned, a much 
greater air-space is needed and a grate, like Fig. 49, is often used. 
The combined area of the holes may be made as great as the 
projected area of the bar, thus giving 100 per cent air-space. 
A dead-plate two inches wide should be fitted to the furnace- 
tube of marine boilers to prevent admission of air at that place. 

The length of fire-bars should not exceed four feet; the 
length of a fire-grate may be made up of two or three short bars. 
Bars are commonly cast in pairs, or three or four may be cast 
together, to resist twisting and warping under heat. 



FURNACES. 



141 



The usual form of grate-bar cast in pairs with lugs at the 
side is shown by Fig. 47. 

The herring-bone grate is shown by Fig. 48; a grate used 
for sawdust, shavings or other inflammable material of this sort 




Fig. 47. 




Fig. 48. 

is shown by Fig. 49. Fig. 50 shows a form of grate designed by 
Prof. Schwamb for burning screenings at a high rate of com- 
bustion. The construction of the grate is shown by the section. 
A boss around each air opening allows ash to collect in the small 




recesses between the air openings on the top of the grate. This 
ash prevents clinkers from adhering to the bars. Bars of this 
sort have been used twenty-four hours a day for over two years 
under boilers forced 80 per cent over rating without trouble. 

Wrought-iron fire-bars are formed with a head and web, 
but are of uniform depth, as they are cut from a rolled bar; they 
are bolted together in sets of six, with washers to give the proper 



142 



STEAM-BOILERS. 



spacing. For marine boilers they may be 5/16 of an inch thick 
at the top, with spaces 3/16 of an inch wide, or less. 




Fig. 50. 

Rocking Grates. — The labor of breaking up the clinker 
which forms on grate-bars is very much reduced by employing 
some form of rocking grate. On locomotives, where the rate of 
combustion is high and where the fire should always be in good 
condition, some form of rocking grate is considered essential 
in American practice. 

In Fig. 51 A and B represent alternate grate-bars which 
are supported at semicircular notches at the ends. CO is a 




b' a' 







Fig. 51. 



cast-iron crank-shaft extending across the furnace at one 
end of the grate-bars. Shallow bars like A rest on cranks 
that are above the line CO, and deep bars like B rest on 



FURNACES. 143 

cranks below that line, as shown at a, a' ', and a" > and at b 
and b' . The further ends of the grate-bars rest on another 
crank-shaft like CO '. At the lower right-hand corner of the 
figure c" represents the end of the crank-shaft and d repre- 
sents an upper crank carrying a shallow bar like A. At g is 
a head to which a lever may be applied to rock the crank- 
shaft. When the crank-shaft is rocked the alternate bars are 
thrown back and forth, and grind up the clinker so that it 
falls through the grate into the ash-pit. 

Firing. — Care, skill, and intelligence are required to burn 
coal rapidly and economically. There is a marked difference 
in the ability of trained firemen to make steam with a given 
boiler, and probably there is nothing more wasteful and costly 
than a poor or careless fireman. 

The method to be adopted in firing depends on the type 
of boiler, the kind of coal, and the rate of combustion. Three 
methods of firing may be distinguished: 

Spreading, which consists in distributing small charges of 
coal evenly over the surface of the fire at short intervals. In 
this method the object is to deliver the coal just where it is 
wanted, and then not disturb it. The fire can then be kept 
in just the right condition at all times, and probably the best 
results can be thus obtained, both in absolute quantity of 
steam and in economy, provided the coal used is well adapted 
to this method. Care must be taken to have the door open 
as little as possible, or an undue amount of cold air will be 
admitted through the fire-door. 

Anthracite coal should always be fired by spreading, and 
should be disturbed as little as possible after it is thrown in 
place. Unless the fire is urged, very little clinker will be 
formed, and the ashes are readily shaken out by a pick or 
hook run up between the fire-bars. The thickness of the fire 
may vary from four to twelve inches, depending on the size of 
the coal and the strength of the fire. 

Dry bituminous coal, and other bituminous coals, if not 



144 STEAM-BOILERS. 

very smoky and if in small pieces, can be advantageously fired 
in this way. Each shovelful thrown on will give off volatile 
matter, which will burn with the excess of air corning through 
the fuel, and very little smoke will result. 

Side firing consists in covering all of one side of the fire 
with fresh fuel, leaving the other bright. The smoke given 
off from the fresh fuel can then be burned with the hot air 
coming through the bright fire. This method of firing is best 
carried on with two furnaces leading to a common combus- 
tion-chamber; the furnaces are fired alternately, at regular 
intervals, with moderate charges of coal. It is customary to 
admit air through the grid in the fire-door when the fuel is 
giving off gas. 

Coking the coal on a dead-plate, or on the grate just inside 
the fire-door, is perhaps the best way of burning a smoky 
coal. The volatile products driven off from the heap of coal 
near the furnace-door burn with the hot air, coming through 
the clear fire at the rear. As soon as the charge is coked it 
is pushed back and spread over the grate, and a new charge 
is thrown on. 

With bituminous coal the fire should be thicker than with 
anthracite coal; from 6 to 16 inches gives good results. 

The method too often followed by ignorant and indolent 
firemen, of throwing on as much coal as the furnace will hold 
and then sitting down to wait till the steam-pressure falls, 
needs to be mentioned only to condemn it. 

Mechanical Stokers, feeding coal regularly from a 
hopper, have been invented in a variety of forms from time 
to time. Since the hopper may be made of considerable 
size, manual handling of the coal may be entirely avoided, 
and one man can easily attend to a number of furnaces with 
little labor and exposure to heat. It would appear also that 
a more even and better-regulated combustion may be had 
than with hand-firing. The primary object, however, is to save 
labor and it is foolish to install a mechanical stoker in a plant, 



MECHANICAL STOKERS. 145 

unless a saving can be made in the cost of labor or the capacity 
of the plant increased. There are many plants equipped with 
mechanical stokers where the hoppers are filled by the shovel. 
Often it is harder to shovel the coal into the hoppers of the stoker 
than it would be to throw the coal on to the grate, and as many 
firemen are needed as would be required to fire the boiler by 
hand. 

With some mechanical stokers working under forced draught 
the capacity of the plant may be increased considerably above 
what could be obtained by hand firing, but, in general, it does 
not pay to use stokers in plants of less than 1500 boiler horse- 
power, as the saving in labor is not great enough to pay for the 
necessary repairs and the interest on the first cost of the stokers. 

The Roney Stoker. — The Roney stoker, shown by Fig. 52, 
as applied to a B. & W. water-tube boiler, may be taken as an 
illustration of a mechanical stoker. The grate-bars extend across 
the furnace and form a serie's of steps down which the fuel slides, 
burning on the way down. Each grate-bar is hung on pivots 
at the ends, near the top, and has a rounded lug at the bottom 
that rests in a groove in a rocker-bar, as shown by Fig. 53. 

The rocker-bar has a slow and regular reciprocation de- 
rived from a small steam-engine, which tips the grate-bars so 
that the upper surfaces are inclined downward to make the 
fuel slide, and then rights them to check the motion of the 
fuel. The coal from the hopper falls onto a horizontal plate, 
from which it is pushed forward by a " pusher " that is driven 
by the steam-engine which drives the rocker-bar. The rate 
of feeding the fuel can be controlled by changing the stroke 
of the pusher, and by regulating the number of strokes of the 
pusher and of the rocker-bar per minute. The ashes, clinker, 
and other unburned refuse collect on a dumping-grate at the 
foot of the grate-bars. This grate is shown in normal position 
by heavy lines in Fig. 53> and in the dumping position by 
light lines. 

This grate appears to be well adapted to burn smoky fuel, 



146 



STEAM-BOILERS. 




Floor Line 



Fig. 52. 



mmm 




Fig. 53. 



MECHANICAL STOKERS. 147 

as such fuel is well coked at the top of the grate, and the volatile 
parts driven off by coking can burn with the excess of air coming 
through the grate at the bottom. 

If the rate of feed is too fast, it is evident that unburned 
coal will work down onto the dumping-grate, and will appear 
in the ashes. If the rate of fuel is regulated so that no coal 
appears in the ashes, the fire becomes thin at the bottom, and 
an excess of air is liable to enter there ; certain tests on this 
grate have indicated such an excess of air, which is the side 
on which the fireman is liable to err, as he may not know 
how much waste he thus occasions, while he can see the coal 
in the ashes. 

Murphy Stoker. — A general view of the Murphy stoker as 
set with a Dutch-oven furnace is shown by Fig. 54. This stoker 
has been one of the most successful of the mechanical stokers 
installed in plants where the service is severe, and where the 
size of the units does not exceed 400 boiler horse-power. 

Coal is fed from the bottom of each magazine onto coking 
plates by a " stoker box " at either side. Each " stoker box " 
is given a reciprocating motion by means of a rack and pinion 
operated through the stoker engine. 

At the bottom of each fuel magazine there is a coking plate 
against which the upper ends of the inclined grates rest. The 
grates are made in pairs, one fixed and the other movable. 
The movable grates, pinioned at their lower ends, are moved 
alternately above and below the stationary grates by a rocker 
bar at their lower ends. 

The feeding mechanism is so arranged that the coal is fed 
faster at the back of the furnace than at the front, thus pro- 
ducing the same thickness of fire at the place where air spaces 
are most likely to occur. 

Any coal that may sift through the grates at the topmost 
point is collected in dust pits on either side of the furnace. 
From these pits the coal is hoed once a day. 

The stationary grates rest at their lower ends upon a grate 



MECHANICAL STOKERS. 149 

bearer which is cast hollow and which receives the exhaust 
steam from the stoker engine. This steam escaping through 
small openings in the grate bearers besides keeping the bearers 
cool, serves to soften the clinker, which together with the ash is 
removed by a rotating clinker crusher located at the centre of 
the furnace between the lower ends of the inclined grate bars. 

Air is supplied to the coking plates through openings in the 
castings against which the fire-brick arch rests. 

Taylor Stoker. — The Taylor stoker is one of the underfed 
type. As it is supplied with air under pressure it is capable of 
being forced so that the boiler may develop three or four hun- 
dred per cent of its rating. Many power plants built recently 
have been planned to work with boilers running normally at two 
hundred per cent of their rating and at times of overload much 
more than this. 

Fig. 55 shows the general arrangement of the stoker and Fig. 
56 gives three views of the furnace and operating mechanisms. 

Coal from the hopper is fed into the retorts from which two 
cylindrical rams in each retort, assisted by gravity, introduce it 
into the furnace at an angle to the fire surface. The upper rams 
push the green coal outward and upward, properly distributing 
it in the coking zone. The action of the lower rams is similar, 
but instead of bringing in fresh coal they push the fuel bed and 
refuse toward the dump plates at the rear. Each retort or 
fuel magazine is formed by two tuyere boxes; that is, the retorts 
and tuyere boxes alternate, the number depending upon the size 
of the boiler. A series of tuyeres is supported on each tuyere 
box, with openings in the vertical faces to distribute air to the 
fuel. These tuyeres, of cast iron, interlock when in position. 

Air for combustion enters the tuyere boxes from the wind box, 
and escaping from the tuyere openings mingles with the gases 
distilled from the coal and with the coked fuel pushed outward 
and upward by the rams. Both rams are actuated by connecting 
rods and links from a crank shaft which is driven from the speed 
shaft. The speed shaft in turn is driven by the fan engine. 



a — 





152 5 TEA M -BOILERS. 

The dump plates, which are combination dump plates and 
fire guards, are hung on the rear of the wind box; these plates 
receive the burned-out refuse and are dumped periodically, as 
the conditions of service may require. The dump plates are 
operated from the front of the stoker, raised, latched in position, 
and released by a hand lever. 

When the Taylor stoker is equipped with extension grates, 
the intermediate grate, which lies between the mouth of the 
retorts and the dump plates, is used as an active grate or for ash 
storage, as conditions may require. The extension grate may be 
rocked, due to its direct connection to the operating mechanism 
of the stoker, the length of travel and position being subject to 
adjustment. 

The air supply to the extension grate is regulated by a hand 
wheel at the front of the furnace, and when once set is subject 
to the same automatic control as the air supply to the stoker 
itself. 

The horizontal distance from centre to centre of retorts is 
2of inches. 

Fig. 57 shows Taylor stokers applied to a new form of boiler 
used by the Detroit Edison Company. This boiler was equipped 
with Roney and with Taylor stokers, and in each case the effi- 
ciency was very high. The tests on this boiler are referred to 
at the end of the chapter on boiler testing. 

The boiler was rated at 2365 horse-power. 

The American Stoker. — This stoker applied to a horizontal 
multitubular boiler is shown by Fig. 58. The grate ordinarily 
used with the boiler is replaced by a shallow iron trough, extend- 
ing nearly to the bridge-wall. The trough is not over one third 
of the width of the regular grate. Fire-brick are laid either 
side of the trough, thus blocking off the grate. Air from a 
blower is sent into the furnace through tuyere blocks located 
near the top of the trough. 

The jets of air issuing from these openings are inclined up- 
wards by a trifling amount. 




Fig. 57. 



(153) 



154 



STEAM-BOILERS. 



Coal is fed from the hopper to a worm rotated at a very slow 
speed by a steam cylinder. 




Fig. 59. 

The coal pushed along by the worm rises through the trough 
and makes a mound which gradually extends on to the brick 
either side of the trough. 

The fire is hottest at the surface of the mound opposite the 



MECHANICAL STOKERS. 1 55 

tuyeres. Any carbon or volatile gases driven off from the green 
coal as it rises through the trough are completely consumed in 
their passage through the hot outer layers. 

Both this stoker and the one shown by Fig. 59 increase the 
capacity of a boiler. Many people do not realize that a boiler 
forced beyond its capacity must be kept clean in order for it to 
last as long as it would if run at normal rating. These stokers 
are good smoke-consumers. 

The ashes and clinkers have to be removed through the fire- 
doors. 

Any stokers to which air is admitted in this way, if improperly 
handled, may give a blowpipe effect. This is due to the air 
escaping through the coal in one spot instead of being distributed 
through the entire mass of coal. The heat generated by this 
action is localized and very intense. 

The Jones Under-fed Stoker. — This stoker, shown by Fig. 59, 
is similar in its action to the American. Air is forced into 
the ash-pit in this case. Coal is forced in intermittently by 
a steam piston. This piston may be operated by a hand-lever, 
or it may be timed to operate as many times an hour as the 
timing device is set for. 

The Green Traveling Link-grate. — Chain grates have been 
used to a considerable extent with the poorer grades of soft 
coal. Fig. 60 illustrates the Green traveling grate applied to a 
Heine boiler. 

Power from a shaft overhead oscillates the vertical rod at the 
left of the cut. A ratchet carried by the arm moved by this rod 
gives motion to a train of gears. The link-grate is moved by 
sprocket-wheels keyed to the shaft at the extreme left of the 
figure. The entire grate and frame may be withdrawn from the 
furnace. 

Columns Supporting Boilers with Stokers. — In many of the 
modern power houses the boilers are located in the story above 
the basement, which is frequently at ground level, thus making 
the boilers 20 feet or more above the ground. 



156 



STEAM-BOILERS. 




MECHANICAL STOKERS. 1 57 

The Stirling boiler and boilers of the Babcock and Wilcox 
type are supported by a steel framework, from which the drums 
are hung, two boilers commonly being set together with one 
common middle wall. 

There are usually, however, three uprights at either end. 

Where the boilers are above the ground it is customary to 
use the steel columns of the building as the uprights at the front 
end of the boilers. 

If two boilers are set with one common wall evidently the 
middle upright may come partly in the brickwork. - 

Boilers which are forced have been known to melt down the 
middle wall near the furnace, and on this account it is not ad- 
visable to have a column act as the middle support. 

The column spacing, for every second bay, may be made 
equal to the width of two boilers, and a pair of channel beams 
strong enough to carry the front ends of the two boilers run from 
column to column. 

The space between sets of two boilers does not need to be 
over 10 feet, and the next column might be located at this dis- 
tance, thus making the column spacing unequal. 

Hanging boilers from channel beams attached to the columns 
brings an eccentric load on the columns which must be taken 
care of by proper bracing, placed between the columns in the 
short span. 

There are other ways of supporting boilers from the columns 
of a building by which an even spacing may be secured, but in 
general the columns are more 'apt to be in the way. 

Smoke Prevention has become a matter of great social 
importance in cities where much smoky coal is used. Though 
the loss through imperfect combustion of carbon to the form of 
carbon monoxide may be great, and though there may be an 
appreciable loss if the volatile parts of coal are driven off un- 
consumed, it is a fact that the loss in smoke, even when it is 
dense and black, is not enough to induce coal users to take 
the trouble to prevent the formation of smoke. Not infre- 



158 STEAM-BOILERS. 

quently it has been found that the methods used to prevent 
smoke are accompanied by a loss instead of a gain. For ex- 
ample, smoke burning by the alternate firing of two furnaces, 
leading to a common combustion-chamber, may give a slightly 
greater efficiency if just enough hot air in excess is admitted 
through the clear fire, to burn the gases distilled from the fresh 
charge. If the clear fire must be kept too thin, and thus admit 
a large amount of air, in order that the smoke may be burned, 
there will be a loss of efficiency. Though it is not well proved, 
it is asserted that the mixture of finely divided carbon, in the 
form of smoke, with carbon dioxide may give a clear gas with 
the formation of carbon monoxide, and thus with a notable loss. 
The same difficulties arise when side firing and coking are re- 
sorted to with smoky fuels. 

One of the most perfect arrangements for smoke prevention 
which has yet been tried, consisted of a detached furnace with 
small grate-area and a deficient air-supply, so that the coal 
was distilled and burned to carbon monoxide; the resulting 
hot gases were then burned under a steam-boiler. The method 
was suggested by the producer-furnaces used for making gas 
for the open-hearth process of steel-making. The objections are 
the loss of heat by radiation from the detached furnace and 
the space occupied by that furnace. Though reported to be a 
success so far as the prevention of smoke was concerned, it does 
not meet with approval. 

It is a common experience that when laws against making 
smoke are enforced users of fuel have chosen to buy anthra- 
cite coal or coke, or in some cases have used crude petroleum 
oil. 

Ringelmann Smoke Chart. — The method of estimating 
smoke proposed by Professor Ringelmann consists in making a 
comparison of the color of the smoke with that of charts of 
different shades of gray. 

The charts are made by drawing a series of horizontal and 
of vertical black lines, 10 mm. apart, on a white ground. 



FURNACES. 159 

The width of the black lines on Chart No. 1 is 1 mm. 
The width of the black lines on Chart No. 2 is 2.3 mm. 
The width of the black lines on Chart No. 3 is 3.7 mm. 
The width of the black lines on Chart No. 4 is 5.5 mm. 
The width of the black lines on Chart No. 5 is 10.0 mm. 

The last card is evidently all black. 

These five charts are placed in a line between the observer 
and the chimney and far enough from the observer so that he 
cannot distinguish the rulings on the charts which appear now 
as four shades of gray and black. 

Generally the charts are placed about 70 feet from the ob- 
server. 

The color of the smoke for any minute is noted by the num- 
ber of chart which matched it for that minute. 

The observations taken each minute are averaged or plotted 
and serve to give one some idea of the amount and grade of 
smoke produced. 

The position of the sun, the background, the condition as to 
weather, the direction and the intensity of the wind, all influence 
the readings. 

Although the method is not entirely satisfactory no better 
one as simple has as yet been suggested. 

Nearly every large city has some " smoke law " which may 
or may not be enforced. 

The law applying to Metropolitan Boston calls for a gradual 
reduction in the amount of smoke allowable. 

All stacks are classified into six classes: 

Class I includes all stationary stacks having an inside area 
at the top not exceeding the area of a circle 5 feet in diameter. 

Class II includes all stationary stacks having an area at the 
top greater than that of a circle 5 feet in diameter but not ex- 
ceeding that of a circle 10 feet in diameter. 

Class III includes all stacks having an area at the top greater 
than that of a circle 10 feet in diameter. 

Class IV includes all stacks of vessels having an inside 



i6o 



STEAM-BOILERS. 



area at the top not exceeding that of a circle 4 feet in 
diameter. 

Class V includes all stacks of vessels having an area at the 
top greater than that of a circle 4 feet in diameter. 

Class VI includes all stacks on steam locomotives. 



TABLE SHOWING THE DENSITY OF SMOKE, IN ACCORDANCE 
WITH THE RINGELMANN CHART, WHICH MAY BE EMITTED 
FROM THE VARIOUS CLASSES OF STACKS AND THE DURA- 
TION OF SUCH EMISSION. 



Class 


I 


2 


3 


4 


5 


6 


Locomotive 

Moving 

Train, 6 Cars 

or More. 


i 




2; 

X, 
U 




d 

O 


03 

c 


6 

u 




c 


6 

O 


o5 
a 


6 

O 


§ 




h 


03 O 

c ai 

d£ 
21 io 


d 
O 


VI O 

On, 

<u • 
(XI C 

d§ 


1910 
1911 

1912 

1913 


3 
3 

2 
2 


6 
4 

8 
6 


4 
3 

3 

3 


5 
10 

6 
3 


4 

•3 

and 

4 

2 

and 

3 

2 

and 

3 


10 

> 20 

5) 

10 ) 

20 ) 
5 ) 


4 
3 

3 

3 


9 
12 

7 
3 


4 
3 

3 

3 


12 
15 

9 

5 


3 
3 

3 

3 


40 
30 

20 

20 


3 
3 

3 

3 


50 
40 

30 

30 



Down-draught Furnaces. — In connection with the subject 
of smoke prevention, attention should be called to down-draught 
furnaces, which have the connection with the chimney below 
the grate. The supply of air is through the fire-door to the top 
of the fire, which has a very attractive appearance, as it burns 
brightly at the upper surface unless obscured by fresh fuel. A 
natural inference is, that the combustion is perfect in a down- 
draught furnace, and that it should give a notable gain in 
economy of fuel, but a little consideration shows that such a 
furnace is subject to the same conditions as an ordinary furnace. 
If there is either an excess or a deficiency of air, the combustion 
will be imperfect; in the latter case, as with an ordinary furnace, 



FURNACES. It) I 

smoke may appear at the top of the chimney. Tests made on 
a boiler using first an ordinary and then a down-draught grate 
have commonly shown little if any advantage in favor of the 
latter. 

Down-draught furnaces, if properly arranged and fired, can 
be made to burn inferior fuels which have a large amount of 
volatile matter without making much smoke; this may be a 
matter of great importance in cities where laws against smoke 
are enforced. 

Hawley Down-draught Furnace. — This furnace consists of 
a water-grate, an ordinary grate beneath the water-grate, and 
an ash-pit beneath this. There are three sets of doors. 

The upper doors are kept open nearly all of the time. Coal 
is fired through the upper doors. The coal next to and in con- 
tact with the water-grate is the hottest, and any volatile products 
driven off from the green coal have to pass downward through 
the water-grate and over the fire on the lower grate before escap- 
ing into the space beyond the bridge-wall. 

The lower grate is supplied with coal which drops through 
the water-grate when the slice-bar is used. This fire is what 
would be called a dirty fire and shows clinkers and ash. 

As a general rule firemen are not apt to keep a sufficient 
depth of fire on this lower grate. A fire about 6 inches thick 
seems to give best results. 

The water-grate adds a large amount of very efficient heating- 
surface to a boiler, and in consequence increases the capacity of 
the boiler without reducing the economy. 

Oil Fuel. — Fuel oil is used for the gener ation of steam to a 
considerable extent in some parts of this country. It has cer- 
tain advantages over coal which may be briefly summarized as 
follows : 

Crude oil has a heating value 30 per cent greater than coal; 
it can be burned without smoke or ash or dust; more perfect 
combustion can be maintained than is possible with coal; a 
greater capacity can be obtained from the boiler; the pressure 



1 62 STEAM-BOILERS. 

in a boiler can be raised very quickly or its power may be doubled 
in a few minutes; the cost of labor per boiler horse-power is very 
low. The disadvantages are the danger of explosions, especially 
with oils of low flash point when handled by an unskilled fire- 
man; the difficulty of storing the oil which must be placed, 
according to city requirements, 30 feet from the nearest building; 
and, on account of the intense heat generated in the furnace, the 
danger of burning the shell of a boiler, if that boiler is supplied 
with feed-water which is of a scale-making quality. 

To burn oil successfully the oil should be heated, atomized, 
sprayed into a fan-shaped jet, and the amount of air should be 
regulated, first, by the hand damper in the flue, and second, by 
opening the ash-pit doors an additional amount when any tend- 
ency to make smoke is noticed. A proper adjustment of the 
burner is necessary in any case. 

As the atomizing of the oil is generally done by means of 
steam it is customary to supply the steam to the atomizer and 
in some cases to the oil pumps through a reducing valve which 
maintains a constant pressure irrespective of any fluctuations 
in boiler pressure. 

Tests made on boilers using liquid fuel have shown a gross 
thermal efficiency of from 79 to 83 per cent with from 1.5 to 2.7 
per cent of the total steam used by the burners. 

A furnace arranged for burning oil fuel is shown by Fig. 61. 
The burners placed just inside the bridge-wall send a fan-shaped 
flame forward. Air is taken in through holes shown at the back 
end of the grate which is covered at the front end as shown. 

Oil Burners. — Oil burners have been divided by the United 
States Naval Liquid Fuel Board into two general classes, each 
class being divided into five types. 

The two general classes are outside mixing and inside mixing 
burners, depending on whether the mixing of the oil and the 
atomizing agent occurs outside or inside the burner. 

The five types into which each class may be subdivided are. 
distinguished by the method by which the oil is atomized. 



OIL BURNERS. 



163 



These are designated as 

Drooling — where the oil oozes out onto the air or steam jet. 

Atomizing — where the oil is swept from the orifice by the 
jet of air or steam. 

Chamber — where oil mingles with steam or air in the body 
of the burner and the mixture issuing from the nozzle is broken 
into minute particles by the expansion of the air or steam. 




Fig. 61. 

Injector — where the action is similar to that of a steam 
injector. 

Mechanical — spraying done mechanically, no atomizing 
agent such as air or steam being used. 

A burner should be designed so as to allow of quick inspection 
and of the easy removal of any foreign material which may clog 
it and of the cheap and rapid renewal of any parts subject to wear. 

A few of the many different makes of burners are shown by 
Figs. 62 to 66. Fig. 62 is known as the Peabody No. 1 burner. 
This is an outside mixing burner of the drooling type, fan-shaped 
flame. 



164 



STEAM-BOILERS. 



The oil pipe is jacketed with steam and provision is made for 
blowing out foreign material which may lodge in the oil pipe with 
steam admitted through a by-pass. 

The tip, shown more clearly by the section, contains two very 
narrow slots separated by a diaphragm, the lower slot being for 
steam, the upper for oil. 




Steam Connection 




Burner Tip 1 



£»<£ 



Oil Connection 



Fig. 62. 



The oil falls at right angles upon the steam jet which atomizes 
it. The mixing and atomizing is done entirely outside the burner. 

The Gem oil burner is shown by Fig. 63. This is an out- 
side mixing burner, drooling type, with rose-shaped orifice. The 
spraying is aided by slight centrifugal action from the internal 
helix. This burner is adapted for use where a very heavy con- 
sumption of oil is required. 

The Hammel oil burner, Figs. 64 and 65, is of the inside 
mixing class and of both the chamber and atomizing types. 
Referring to Fig. 64, oil enters at the left through the inclined 
passage into the mixing and atomizing chamber at the right-hand 
end of the burner. Steam enters the lower chamber and flows 
through three small slots, one of which is shown in the section, 
into the mixing chamber where it meets the oil. A plan view 
of Fig. 64 would show that the mixing chamber was V-shaped, 
with the long narrow opening at the front end. 



OIL BURNERS. 



I6 5 



The Texas oil burner, shown by Fig. 66, is of the inside mix- 
ing class, chamber type. As the oil flows into the large mixing 
chamber it is picked up by the 
steam to which rotary motion has 
been imparted by a short helix 
in the steam passage just back of 
the oil inlet. The mixture then 
passes along the chamber through 
a spiral passage occupying about 
one half of its length, which sets up 
a strong centrifugal action which 
causes the oil to be thoroughly 
atomized and vaporized when it 
issues from the fan-shaped orifice 
in the small chamber at the tip of 
the burner. This orifice is made to 
give any width of flame required 
and the tip is easily renewable in 
case of wear. 

A discussion of oil burning is to 
be found in the journal for August, 
ion, of A.S.M.E., in an article FlG - 6 ^ 

by Mr. B. R. T. Collins. From this article much of the pre- 
ceding has been abstracted. 

Induced Draught and Forced Draught. — When a higher rate 






Fig. 64. 



Fig. 65. 



of combustion is required than can be had with natural draught, 
resort is had to forced draught, by aid of which 150 pounds of 
coal can be burned per square foot of grate-surface per hour. 



1 66 STEAM-BOILERS. 

Three systems of forced draught are in common use, namely, 
with a closed stoke-hole, with closed ash-pits, and induced draught. 

Induced draught has long been used on locomotives, by the 
action of the exhaust-steam thrown through the smoke-stack. 
The same method is used to some extent on tug-boats. This 
method is simple and effective, but can be used only with non- 
condensing engines. Induced draught may be obtained by a 
centrifugal, or other form of blower, in the chimney. It is 
essential that an economizer should be used to cool the gases 
before they come to the blower. 

On steamships forced draught has been obtained by the aid 
of centrifugal fan-blowers. The method with closed ash-pit 




Fig. 66. 

has been used with success on merchant steamers and some 
war-ships. With this method air drawn from the fire-room 
passes through a blower and is delivered to the ash-pit, which 
has an air-tight door. If the pressure in the ash-pit exceeds 
the resistance to the passage of air through the fuel, flame comes 
out around the fire-door unless it is also made air-tight. When 
the fire-door is opened to throw on coal the blast must be shut 
off from that furnace and all others having a common combustion- 
chamber, or flame will shoot out into the fire-room in a dangerous 
manner. One reason why it has not been used on war-ships is 
the difficulty of properly ventilating the many small fire-rooms 
in which boilers are placed. 

The closed stoke-hole has been the customary way of getting 



FURNACES. 167 

a forced draught on torpedo-boats and on other naval vessels. 
The stoke-hole is closed air-tight, admission and egress being 
through air-locks, and air from without is forced in through a 
centrifugal blower till the pressure exceeds that of the atmos- 
phere. When a fire-door is opened to attend to the fire, there 
is a strong inrush of air that is liable to make the tube-plates 
leak. So great difficulty has been experienced from this cause, 
when forced draught has been used with the Scotch boiler, that 
many naval officers doubt its advisability for large ships. The 
success of forced draught on the locomotive and on torpedo- 
boats with modified locomotive-boilers may be attributed partly 
to the type of the boiler and partly to the fact that there is only 
one boiler and one furnace. When two boilers are used on a 
torpedo-boat, each has its own chimney. 

On locomotives the induced draught is frequently equiva- 
lent to a column of water 5 or 7 inches high. Forced draught 
on torpedo-boats has approached these figures, but is usually 
less. Large ships usually have the forced draught restricted 
to 2 inches of water. On account of the resistance to the 
entrance of air to the fire-rooms of war-ships, through venti- 
lating shafts, gratings, etc., it has been common to assist the 
draught by running the blowers without closing the air locks. 

The increased cost of coal has led many to burn screenings or 
buckwheat coal by means of a forced draught. 

A blower driven by a steam-engine supplies air to the ash-pit 
at from 1/2 to 4 inches water pressure. A rapid rate of com- 
bustion is maintained, and even though the cheap coal is not 
burned as economically as it might be, still the poorer coal at 
the present prices shows a saving in the cost of making steam. 

The speed of the engine driving the blower is controlled by 
the pressure in the boiler, a damper regulator operating the 
throttle of the engine. When the damper regulator has closed 
the throttle, the engine is kept turning fast enough to pass the 
dead-centers by steam admitted through a small pipe with valve, 
which by-passes the throttle controlled by steam pressure. 



1 68 



STEAM-BOILERS. 



In the induced draught system, as arranged in large plants, 
the gases are drawn from the grate through an economizer into 
the exhaust-fan, which then discharges the gases at about 300 F. 
into the stack. The stack serves simply to carry the gases away. 

Howden's System. — The temperature of gases in the up- 
takes of marine boilers is frequently high, especially when forced 
draught is used. In Howden's system the products of com- 
bustion pass through vertical transverse tubes placed in an 
enlargement of the uptake. Air to supply the fire is forced over 
these tubes by a fan-blower and is thereby warmed, thus saving 
heat and giving quicker combustion. Care must be taken in 
using this system not to go too far, or the fire may become too 
hot and rapidly burn out the fire-grates and do other injury. 

Fire Cracks. — Fire cracks are often found on old boilers at 
the joints exposed to the fire. The two rivets at the left in 
Fig. 67 show such cracks. 




Fig. 67. 

These cracks are caused by the repeated buckling, between 
the rivets, of the plate exposed to the fire. This plate becomes 
much hotter than the plate back of it which is in contact with 
the water in the boiler, and any change in the temperature of 
the fire is felt by the plate. 

Innumerable repetitions of this action ultimately starts a 
crack which extends as shown. If a crack extends beyond a 
rivet it should be plugged to prevent the crack from extending 



FURNACES. 169 

to the edge of the lap of the other plate. This plug is a piece of 
soft copper driven into a hole drilled about 3/8 inch diameter. 

The cracks are most always at the rivets, but sometimes a 
crack will be found between two rivets. 

In case a fire crack should leak much the leak may be stopped 
for a time by countersinking the plate, as shown by the right- 
hand rivet and driving in a very soft rivet. The metal of the 
rivet will flow out into the crack. • 

Cleaning Fires. — Three tools are used in clearing the grate: 
they are a long straight bar known as the slice-bar, a similar 
bar with the point bent at right angles to make a hook, and a 
long-handled rake with three or four prongs. The hook may 
be run along between the grate-bars from below, to clear the 
spaces from ashes and clinker. The slice-bar is thrust under 
the fire on top of the grate to break up the cinder; it is used also 
to stir and break up caking coals. The rake is used to haul the 
fire forward or to draw out cinder. 

To clean a fire the fireman breaks up the cinder with the slice- 
bar and rattles down the ashes; if necessary, he works the fire 
back toward the bridge and exposes the grate in front, which 
may then be thoroughly cleaned. Then he hauls the fire forward 
and cleans the back end of the furnace. Cinder which will not 
break up and pass through the grate is pulled out through the 
fire-door. Some firemen prefer to clean the grate one side at a 
time. After the grate is cleaned the fuel left is spread evenly over 
the grate and fresh fuel is thrown on. The fire should be allowed 
to burn down before cleaning, but a fair amount of glowing 
coal should be left to start a new fire briskly. Before beginning 
to clean the fire the draught should be checked by closing dampers 
or otherwise. 

Economizers. — An economizer cons sts of a series of vertical 
cast-iron tubes placed in the flue of a boiler between the boiler 
and the stack, and used to heat the feed-water with heat re- 
covered from the flue gases (Fig. 68). 

Any heat taken up in this way is just so much heat gained, 



170 STEAM-BOILERS. 

provided the draught is not so reduced by the extra resistance 
offered to the passage of the flue gas as to lessen the capacity 
of the boiler. 

An economizer will show a greater saving on a plant which is 
forced than on a plant which is running at a moderate rate. 
Ordinarily a gross saving in coal of from 8 to 10 per cent will be 
made. It is not advisable, however, to install economizers in 
small plants unless these plants are being forced. 

To find whether or not an economizer will make a net saving, 
the interest on the money invested in the economizer and the 
amount allowed for its depreciation must be deducted from the 
gross saving. 

The life of an economizer is generally taken as 20 years, and 
the cost is from $4.25 to" $4.50 per boiler horse-power." From 
3.5 to 5 square feet of economizer surface are commonly allowed 
per boiler horse-power. 

Economizers are made up of cast-iron tubes about 4 inches 
in inside diameter and 9 feet long. The tubes are turned at 
the end to a slight taper and are forced into top and bottom 
headers by hydraulic pressure. These headers are made to take 
different numbers of tubes, as is shown by the table of dimen- 
sions given in the Appendix. The lower headers project through 
the brick-work housing and are joined together by a " bottom 
branch pipe " running lengthwise of the economizer. This 
" bottom branch pipe " has on one side a series of flanges for 
making the connection with the bottom headers, and, on the 
opposite side, a series of clean-out openings, one opposite each 
header. Expansion of these connecting pipes at the bottom and 
at the top is provided for by U-shaped bends, as shown in Fig. 
68. The feed- water enters this " bottom branch pipe " at the 
end of the economizer nearest the chimney and leaves the econo- 
mizer at the top, at the end nearest the boiler. The top headers 
are similarly connected. This pipe joining the top headers is 
placed above instead of at the end of the header and at the 
opposite side of the economizer. In some cases means are pro- 



172 STEAM-BOILERS. 

vided for washing out the bottom headers, by sending a stream 
of water from a hose down through the tubes at the back end of 
the bottom headers, and letting it flow along the entire length 
of the bottom headers and out through the clean-out openings 
directly opposite the headers. 

In setting up an economizer, room should be left opposite 
these clean-out openings, so that a scraper can be put into each 
header to remove any scale which may lodge there, inasmuch as 
the headers are sometimes cleaned out in this way, instead of by 
washing. 

In order to repair a tube and replace it by a second tube 
without dismantling that section or that header, a slot is made 
in the upper end of the tube with a chisel, so as to enable the 
tube to be sprung together. The tube is then withdrawn from 
the bottom header in the following manner. 

A piece of iron, shaped as shown in the cut, is pushed down 
inside the tube and moved to one side so as to engage the bottom 
end of the tube, this piece being held by a rod with thread and 
nut at the top. A second piece like a wedge is held against the 
first piece. By screwing on the first nut the tube may now be 
withdrawn from the bottom header. The new tube is now in- 
serted, driven into the bottom header, and a conical wedge used 
to make the joint between the tube and the top header. Some- 
times a tube which has given trouble may be plugged and cut 
out of service. 

As broken tubes are withdrawn through the top of the 
economizer or in case of serious mishap, as the entire section is 
taken up through the top of the economizer, there should be 
sufficient room left over the economizer to allow for this. The 
arrangement of the brickwork should be such as to enable a 
section to be withdrawn without making it necessary to take 
down a large amount of masonry. 

The heating surface needed may be put either in one large 
economizer, through which all the gases from all of the boilers 
pass, or there may be a number of smaller economizers, known 



ECONOMIZERS. 173 

as " unit economizers," one for each battery of two boilers. With 
the first arrangement, any accident to the economizer which 
might put it out of service would reduce the power of the boiler 
plant 8 or 10 per cent. The draught would be reduced to a con- 
siderable amount by this arrangement. 

In the second arrangement, as only one unit would be cut 
out, in case of accident, the reduction in power of the boiler 
plant would be inappreciable. 

The flue gas leaving the boiler should have a direct passage 
to the chimney around the economizer. Suitable dampers should 
be provided so that the gases may be sent either through the 
economizer or directly to the chimney. When the economizer 
is out of service both dampers at entrance and exit to the econo- 
mizer should be closed. 

Reducing the temperature of the flue gas by passing it through 
the economizer reduces the draught practically in the proportion 
that the absolute temperature of the flue gas is reduced. The 
draught is still further reduced by the friction of the gas in 
passing through the economizer, and, in the many instances 
where the draught is poor, it would be unwise to install an econo- 
mizer unless an induced draught fan were to be installed also. 
This loss of draught varies from 0.2 to 0.4 inch according to 
conditions. For ordinary cases 0.3 inch may be assumed as 
the loss. 

Usually on the side of the economizer there is a space about 
1 2 inches wide left between the last tubes and the casing or brick- 
work, to allow of inspection. Sometimes there are two such 
passages, one either side of the economizer. These passages are 
closed by side dampers when the economizer is in use. 

Provision should be made for removing the soot from the 
bottom of the economizer. To remove the soot which collects 
on the tubes, scrapers are provided, these scrapers being in the 
form of loose collars which are alternately raised and lowered by 
chains operated from a shaft running along the top of the econo- 
mizer. If the economizer is only eight tubes wide, one shaft will 



174 STEAM-BOILERS. 

serve, but if the economizer is ten or twelve tubes wide there 
should be two sets of shafts. 

The economizers must each be provided with a relief valve 
of sufficient size and with a blow-off valve. Two arrangements 
of economizers as applied to two types of boilers are shown by 
Figs. 69 and 70. 

Sometimes economizers become " steam bound," due to 
steam being generated in the tubes. This may happen if the 
feed pump has been stopped for any length of time while the 
boilers were running. If the economizer is steam bound it is 
difficult, or almost impossible, to get water through it, and the 
thumping and snapping which results is liable to start some of 
the joints. 

The economizer is always connected to the feed line in such a 
way that the feed may be by-passed around the economizer, and 
when the economizer becomes steam bound it should be cut out 
and allowed to cool until the steam has condensed. 

The rise of temperature of the feed-water in the economizer 
may be calculated as follows : 

Calculation of an Economizer. — 

T h = temperature of flue gas entering economizer. 
T c = temperature of flue gas leaving economizer. 

t h = temperature of feed-water leaving economizer. 

t c = temperature of feed-water entering economizer. 
0.24 = specific heat of flue gas. 
30 = number of pounds of water fed per boiler horse-power. 
24 = pounds of flue gas per pound of coal. 

9 = probable evaporation of water per pound of coal. 

(T h - T c ) X 24 X ^ X 0.24 = 30 (t h - 
9 

T h - T c =-~ (t h - = 1.562 (h - 
0.64 

. T,= T h -1.562(4-0. 



ECONOMIZERS. 175 

For different evaporations, or for different weights of flue gas 
per pound of coal, the value to replace 1.562 may be easily figured. 
As the coldest gas is at that end of the economizer at which the 
cold water enters, and the hottest gas at the end where the water 
is hottest, there can be but little error in taking the difference 
of the mean temperatures of the gas and of the water. 

Let S = square feet of heating surface in the economizer per 
boiler horse-power or per 30 pounds of feed-water fed per hour. 

Let 3 = B.T.U. transmitted per square foot of surface per 
hour per degree difference of temperature between the gases out- 
side the tubes and the water inside the tubes. This value 3 
would apply to a new economizer; as the metal gets old the inter- 
change of heat would be less, even as low as 2 B.T.U. per hour 
per square foot per degree difference in temperature. 

30 (4 - = (^^ - '-^x 3 x 5 

■^(h -t c )=SlT h +T h - 1.562 (4 - ~k- h\ 

O _ h ~ tc 

2 T h - 1.562 (t h -t c ) -t h -t c 
2ot h - 2ot c = S U T h - 1.562 (t h - /,) - t h - t c \ 



_ 20 t c -f 2 ST h -f- 1.562 St c — St c 
20 + 1.5625 + 5* 



_ 20 t c -f 2 ST h + 0.562 St c 
20 + 2.562 6" 
The Green Economizer Company use the following formula: 

S(T h -t c ) 



k - L 



-+(^* 



In this w = pounds of feed-water per boiler horse-power. 

G = pounds of flue gas per pound of combustible. 

C = pounds of coal per boiler horse-power hour. 
This formula is practically the same as the one already worked 
out. 



176 STEAM-BOILERS. 

Illustration. — Flue gas leaves a boiler and enters an econo- 
mizer at 550 F. The feed- water after passing through both a 
primary and a secondary heater enters the economizer at 200 F. 
What is the temperature of the feed-water leaving the economizer? 

What is the temperature of the flue gases leaving the econo- 
mizer? 

Assume in this case 4 square feet of heating surface in the 
economizer per boiler horse-power. 

_ 20 X 200 -f 2 X 550 X 4 + 0.562 X 4 X 200 
20 + 2.562 X 4 

k = 2Q2° 

T c = 1.562 (292 — 200) = 407 . 

The flue gas has been reduced 143 , and the feed-water in- 
creased in temperature from 200 to 292 . 

Figs. 69 and 70 show two different arrangements of Green 
economizers. 

Fans for Induced Draught and for Forced Draught. — As has 
been pointed out in the discussion of economizers, the cooling 
of the gases and the frictional resistance offered by the econo- 
mizer both tend to reduce the draught, and, in most cases, it is 
inadvisable to install an economizer unless an induced draught 
is maintained either by a centrifugal fan or by some other 
means. 

A centrifugal fan consists of a series of paddles rotated in a 
casing. Air is drawn in at the centre of the casing, around the 
shaft, either on one or on both sides, and is delivered at an out- 
let in the periphery. 

If the vanes of the fan be revolved at a certain speed with the 
end of the discharge pipe closed, the pressure produced in the 
pipe is the maximum possible at that speed. This pressure is 
frequently called the dynamic pressure. If, now, an outlet be 
made in the closed pipe, the fan will maintain this same total 
pressure until a certain area of opening is obtained. This area 
is called the " capacity area," or " blast area," and is approxi- 



k#^mwM»^^ 




i 7 8 



STEAM-BOILERS. 




CROSS SECTION 



Fig. 70. 



FANS. 



179 



mately equal to the diameter of the fan in inches times the width 
in inches, divided by three. 

The " capacity area " depends somewhat on the shape of the 
discharge outlet. The " capacity area " for a hole in a flat plate 
is greater than that for a tapered discharge pipe. 

The power required to drive a fan with the outlet closed is 
from 30 to 37 per cent of that required when discharging through 
an opening equal to the " capacity area." 

Suppose that three glass U tubes, shaped as shown at a, b, 
and c in Fig. 71, be inserted in the discharge pipe of a fan. The 
tube a opens at right angles to the axis of the pipe. The tube b 




\CONTRACT£D 
J>/3CHARQ£. 



Fig. 71. 

has its opening pointing along the axis of the pipe and towards 
the fan, and the tube c has two openings, one like b and one 
like a. 

If the end of the discharge pipe is closed and the fan be run, 
the pressure in the discharge will cause the water in the U 
tubes a and b to rise in the legs open to the air. The readings 
of a and b will be the same. The level in c will show no change. 
If the end of the discharge pipe be opened, the pressure shown 
by a decreases, that shown by b remains nearly constant, 
and that shown by c is equal to the difference between b 
and a. 

On account of eddy currents, etc., the dynamic pressure shown 
by the U tube b is somewhat less for a moving column of air 



180 STEAM-BOILERS. 

than for a still column such as is obtained with a closed dis- 
charge. 

The pressure shown by b is called the " dynamic pressure " 
(D.P.), that by a the " static pressure " (S.P.), and that shown 
by c the " velocity pressure " (V.P.). 

Evidently (D.P.) - (S.P.) = (V.P.). If the velocity pres- 
sure is known the velocity may be calculated from 

V = V 2 gh, 

where h equals the height in feet of a column of air at the same 
temperature as the air in the pipe, which will produce a pres- 
sure equal to the velocity pressure. V = velocity in feet per 
second. 

, _ 144 X velocity pressure X 0.036 

* _ ~ T ' 

where d equals the density of the air at a pressure corresponding 
to the static pressure and 0.036 is the pressure of an inch of 
water on a square inch area. 






144 X velocity pressure X 0.036 , x 

d 



5.2 velocity pressure , , 

d 



velocity pressure = — (3) 

or the velocity pressure increases as the square of the velocity. 
The dynamic pressure increases also as the square of the velocity. 
The work done on the air per second is very nearly equal to 
the pressure on the square foot times the volume displaced per 
second plus the kinetic energy due to the velocity which has 
been imparted. 

Static pressure X 0.036 X 144 X V X a -\ V 2 . (4) 

a = area of discharge at the point where velocity V is measured. 



FANS. 181 

Substituting for V 2 from equation (i) in the last term of (4), 
V X a X d 2 g X 144 X velocity pressure X 0.036 
2g d 

This last term simplifies to the velocity pressure X 0.036 X 144 
X V X a, which substituted in equation (4) gives: 
(static pressure + velocity pressure) X (0.036 X 144) XV Xa. (5) 
This evidently is equal to the dynamic pressure on the square 
foot times the volume moved. 

As the dynamic pressure varies with the square of the 
velocity, it is evident that the work increases with the cube of 
the velocity. 

To measure the velocity pressure, various forms of Pitot 
tubes have been used. Those made of bent glass are not reliable. 
A form used by Mr. D. W. Taylor is described in the Proceedings 
of the Naval Architects and Marine Engineers, November, 1905. 

It is substantially as shown by Fig. 72. Mr. Taylor made 
extensive tests on different types of fans. He found the efficiency 
of the fans tested to vary from 30 to 45 per cent, according to the 
speed and the delivery pressure. He deduced also by experi- 



73-o.» Tube ffl.Ml'j^ V«/f* | 



T — 1 ' 1 . 1 rfr 

I A S/ct Zf'Long ,„ Outer ' 



I 

I 



PITOT TUBE. 



I iMBS TO J 1 

^_JM/IHOM£ TO\ ' I 

01 



Fig. 72. 

ment the value of the coefficient of friction in round galvanized 
iron pipes as it applies in the formula 



D 3600 

H f = loss of head in feet of air due to air friction. 
D = diameter of pipe in feet. 
L = length of pipe in feet. 
F = velocity in pipe in feet per minute. 
/ = 0.00008 by experiment. 



182 STEAM-BOILERS. 

Substituting this value and reducing, 

L F 2 

H f = ± ~ (6a) 

D 11,250,000 

For rectangular pipes where Y = short side in feet and nY — 
long side in feet, the formula becomes 

H L±nA_FL_ . . . (6b) 
n Y 22,500,000 

L = length of pipe in feet and F = velocity in feet per 
minute. 

A number of years ago Mr. F. R. Still of the American Blower 
Company wrote an article which appeared in the Journal of the 
Western Society of Engineers, 1902, on the performance of steel- 
plate fans. The curves shown by Fig. 73 are taken from that 
article. 

The letters (P.V.P.) mean peripheral velocity pressure; the 
other letters (D.P.), (S.P.), and (V.P.) are used to denote 
dynamic pressure, static pressure, and velocity pressure, as 
before. 

The curve marked K was plotted by an empirical formula. 
This curve is made use of in calculating the inlet area of an 
induced draught fan such as would be used for flue gases. 

'-? « 

/ = area of fan inlet, square feet. 
n _ volume of gas per minute 

1000 
H = draught in inches of water. 

K = constant determined by experiment (to be taken 
from plot). 

The ratio of opening as ordinates means the percentage of the 
actual opening compared with that of the opening needed for 
free discharge, this being generally somewhat greater than the 



FANS. 



183 



Tiatio, of Openina., Te?- Cent. 
* ^ & X» * 




Fig. 73. 



184 STEAM-BOILERS. 

"capacity area." The ratio of effect in per cent due to restrict- 
ing the discharge area is plotted as abscissae. 

From the plot it is seen that with a full opening the ratio 
of (V.P.) to (D.P.) = 1, or the (D.P.) = (V.P.). The static 
pressure (S. P.) for full opening = (D.P.) — (V.P.) = o. 

Suppose the opening to be restricted to 70 per cent of its full 
area, then 

(S.P.) = (D.P.) - 0.22 (D.P.) = 0.78 (D.P.) 
(S.P.) is also 0.62 (P.V.P.) 

The following tables are taken from " Mechanical Draft " 
by the B. F. Sturtevant Company. 

V is calculated by equation (2), page 180, the value of d 
appearing in that equation being calculated thus: 

14.7 X 12.39 _ (i4-7 + (S-P-) X0.036) Xvolume _ 1 = , 

49 J -5 459- 1 +5° ' volume 

The multiplier for different temperatures is found by noting 

that the velocity varies as -, and d varies inversely as the abso- 

d 

lute temperature, d for 70 would be 5 = 0.06 times the 

529-5 
value at 50 . 

1 



0.96 



= 1.02, as found in the table. 



P 
As the velocity V varies as \ — the relative pressure necessary 

r a 

to produce the same velocity may be found thus : 

Taking 70 as before, = VP = V0.98 = 0.96, as given 

1.02 

in the table on the following page. 



FANS. 



185 









Static Pressure 






of Still Air or 


Velocity of Dry Air at 50 ° F. 


of Still Air or 


Velocity of Dry Air at 50 F. 


Velocity Pres- 






Velocity Pres- 
sure of Moving 






sure of Moving 










Air in Inches of 


Feet per Sec. 


Feet per Min. 


Air in Inches of 


Feet per Sec. 


Feet per Min. 


Water. 






Water. 






O. I 


20.72 


1243 


0.9 


62. IO 


3726 


O. 2 


29 


30 


1758 


I .0 


65-45 


3927 


0.3 


35 


84 


2150 


I . I 


68.48 


4118 


O.4 


4i 


43 


2486 


I . 2 


71.68 


43° 1 


o-5 


46 


31 


2779 


1-3 


74.60 


4476 


0.6 


50 


73 


3043 


1-4 


77-41 


4645 


0.7 


54 


78 


3287 


1-5 


80.12 


4807 


0.8 


58 


56 


3514 









If the air is at a temperature different from 50°, the velocity 
may be obtained by multiplying by the values given in the 
following table. 



Temperature of 
Air, ° F. 


Relative Ve- 
locity due to 
Same Pressure. 


Relative Pres- 
sure Necessary 
to Produce 
Same Veloc- 
ity. 


Temperature of 
Air, ° F. 


Relative Ve- 
locity due to 
Same Pressure. 


Relative 
Pressure Nec- 
essary to 
Produce 
Same Ve- 
locity. 


30 


O.98 


I .04 


200 


I. 14 


O.78 


40 


O.99 


I .02 


250 


I 


18 


O.72 


50 
60 


I .OO 
I .OI 


I .OO 
O.98 


300 
350 


I 
I 


22 
26 


O.67 
O.63 


70 


I .02 


O.96 


400 


I 


30 


0-59 


80 


I.03 


O.94 


450 


I 


34 


0.56 


90 


I .04 


0.93 


500 


I 


37 


0-53 


IOO 


I 05 


O.91 


550 


I 


4i 


051 


I50 


I .09 


O.84 









Suppose that it is desired to find the horse-power input to a 
fan in order for it to maintain a velocity of 3927 feet per minute 
through a restricted opening having an area 70 per cent of the 
capacity area which may be taken as 4 square feet. The air 
may also be assumed to be 70 in temperature. 

Referring to Still's curves: 

(V.P) f 

, v =0.22 for 70 per cent opening. 



1 86 STEAM-BOILERS. 

From the table it appears that air at 50 under 1 inch velocity 
pressure will give velocity 3927, and at 70 the pressure required 
is 1.0 X 0.96 = 0.96 inch. 

(V.P.) 0.96 . - 

(D^) = (D^) = °- 22 mGh 

(D.P.) = 4.364 
4.364 - 0.96 = 3.404 = (S.P.) 

„ 3927 X 2.8 X 4-364 X 144 X 0.036 
Horse-power = Q2 — - ^2_^± ^t q_ __ T g^ 

33,000 X 0.42 

The use of the curves may be best explained by showing their 
application to a few cases. 

Suppose a fan to deliver 10,000 cubic feet of air per minute 
against a dynamic pressure of 1.33 inches, the discharge area 
being restricted 80 per cent. 

The mechanical efficiency is 37 per cent. 

rri, u 10,000 X 1.33 X 5.2 , 

The horse-power = — — = 5.67. 

33,000 X 0.37 

The ratio of (D.P.) to (P.V.P.) for 80 per cent opening is 0.66, 
hence 

(1 ^_ = o.66; (P.V.P.) = ,00 inches; ^ = f^ = °.4 5 ; 

(S.P.) = 0.90 inch; ^ ^^ = 0.22; (V.P.) = 0.44 inch; 
(D.P.) - (S.P.) = (V.P.) = 0.43 inch. 



If the outlet is now opened sufficiently to give an unrestricted 

discharge, A ' '\ = 0.33, or ' = 0.33; whence (V.P.) = 
(r.x.r.) 2.00 

0.66 inch; (D.P.) = 0.66 inch; (S.P.) = o inch. 

The volume moved is of that n 

0.80 

efficiency of the fan becomes 22 per cent. 



The volume moved is of that moved before, and the 

0.80 



FANS. 187 



10,000 X — — X 0.66 x 5.2 

r^ , O.OO 

The horse-power = 5.91. 

33,000 X 0.22 

If the opening is now restricted to 20 per cent, the capacity 

becomes 2500 cubic feet per minute, and the dynamic pressure = 

. , . (D.P.) 

2.10 inches since = 1.15. 

2.00 

m * . , (S.P.) (S.P.) 

The static pressure = 2.26 inches since , = 

(r.V.P.) 2.00 

= I.I3- 

The velocity pressure = 0.04 inch. 

The efficiency of the fan is 27 per cent and the power is 

tt 2 5°° X 2 -3° X 5- 2 ^ 

Horse-power = -* Q *- = 3.36. 

33,000 X 0.27 

Should the outlet be entirely closed, the power is 37 per cent of 
that required for an unrestricted discharge, or 0.37 X 5.91 = 2.19 
horse-power, and the static pressure, which is, in this instance, the 

same as the dynamic pressure, is 2.32 inches since ' = 1.16. 

2.00 

The following example will illustrate the method of making 
the calculations for an induced draught fan. 

Example. — Determine the size of an induced draught fan and 
the approximate power required to drive it for a boiler plant of 
2000 boiler horse-power. Heating value of coal 14,650 B.T.U. 
per pound. Boiler efficiency 70 per cent. Flue gases leaving 
economizer and entering fan 400 F. Draught as shown by a 
U tube 1 .00 inch. 

Then 33*47 = 6^27 pounds of coal per hour. 

14,650 X 0.70 D ' F * 

The volume of a pound of flue gas at 400 F. is approximately 

X 11.78 = 23.0 cubic feet. Allowing 21 pounds of air at 
49i-5 
the ash-pit per pound of coal, and assuming 5 per cent leakage 



1 88 STEAM-BOILERS. 

into the setting, makes 22.05 pounds of air per pound of coal; 
and inasmuch as the coal is 90 per cent carbon, there results 22.95 

pounds of flue gas per pound of coal. — — j 1 ^—*- 

60 

= 57,530 cubic feet of gas entering fan per minute. It is cus- 
tomary, when little is known about a plant in which a fan is 
to be installed, to assume that the resistance is equivalent to 
restricting the discharge outlet 25 per cent. Hence, in this 
problem, the various factors are referred to a " ratio of open- 
ing " of 75 per cent. 

From formula (7), page 182, the area of the inlet should be 

/ = — ^ = 5 57-53 = 27.9 square feet, 

H 1 

which corresponds to a diameter of 5.96 feet. (K = 0.485 is 
taken from the curve (Fig. 73).) 

The area of the inlet may be taken as 40 per cent of the area 
of the side of the wheel. The latter then will be 

— ^ = 69.7 square feet, 
0.4 

which corresponds to a diameter of 9.42 feet. 

Referring to Fig. 73, the ratio of dynamic pressure to 
peripheral velocity pressure, (D.P.) to (P.V.P.), at 75 per cent 
opening is 0.73. 

rru *• (S.P.) 

(P.V.P.) = °' 53 ' 
(D.P.) 



(P.V.P.) Q.73 = , . (P- p -) 
(S.P.) 0.53 x * 37 (S.P.) 

(P.V.P.) 

As (S.P.) in this particular case is 1; (D.P.) = 1.37 inches 

(D.P.) - (S.P.) = (V.P.) = 0.37 inch. 
The power required to drive the fan 

= 57,53o X 1.37 X 5-2 = H p 
33,000 X 0.4 



FANS. 189 

The hot gas leaving the fan and entering the chimney is 
usually at less than atmospheric pressure, and the draught due 
to this column of hot gas reduces the work on the fan. 

In the case of an induced draught, the static pressure shown 
by the U tube a, Fig. 71, being less than atmospheric, the level 
of water stands higher in the inner leg than in the open leg. If 
one were to imagine the open legs of the tubes a and b, Fig. 71, 
sealed and exhausted of air, then, if the tubes were of sufficient 
length, the difference in water level would measure the absolute 
pressure; the differences between the absolute (D.P.) and (S.P.) 
would be positive and a measure of the (V.P.). In any case, the 
tubes c and d, as connected, measure the (V.P.). 

The peripheral velocity is 

V = V2 gh, where h is expressed in feet of gas. 

h = 1.37 X 62.4 = 1.37 X 5-2 
12 0.0413 

24.2 



/ I "^7 X ^ 2 

V = v 2 £-^ — = 10=5.2 feet per second or 

V 0.0413 

6312 feet per minute. 

57j>53_ _ g H S q Uare f ee t for " blast area." 
6312 

The blast area is one third of the product of the diameter 
and the width; hence the width of the blades of the fan is 

<^lXi =2 . 9fee t. 

9.42 

The speed is ^ = 213 R.P.M. 

9.42 X3.1416 

The efficiency of the fan has been taken as 40 per cent f ror 1 
the curves shown by Fig. 73. 

On account of the draught exerted by the chimney, the work 
needed to drive the fan would be somewhat less than 31 H.P. 



190 STEAM-BOILERS. 

If the fan were engine-driven by an engine using 55 pounds 

of steam per indicated horse-power per hour, or -^ =61 pounds 

0.9 

per horse-power output (the mechanical efficiency of the engine 
being 90 per cent) , then the steam consumption of the fan engine 
would be 61 X31 = 1 89 1 pounds per hour. Assuming that 30 
pounds of water, under the conditions of pressure and tempera- 
ture of feed, would, if evaporated per hour, be equivalent to a 
boiler horse-power, then the per cent of the total boiler horse- 



power required by the fan is — — X 100 = 3.15. 

2000 

If, now, the fan were motor-driven, and the current cost 18 

pounds of steam per engine horse-power input to the generator, 

and if the generator and the motor each had an efficiency of 90 

per cent, then the percentage input to the fan would be 

18 X 31 . 

"5- 30 

O.9X0.9 

— - X 100 = 1. 15. 

2000 

Arrangement of Induced Draught Fan and Economizer. — 

The boiler plant of the Eastman Kodak Company is arranged 
as shown by Fig. 74. The induced draught fans, which are 
in duplicate, may draw the gas from five vertical boilers 
through either economizer, or by closing a damper in the main 
flue the fans may draw the gas from three boilers through one 
economizer and the gas from two boilers through the other 
economizer. 

In case of an accident to an economizer the first arrangement 
would be used. 

It is possible also to cut out both economizers and to run the 
gases directly into the stack either with or without the help of 
the induced draught fans. 

Another arrangement is shown by Fig. 75, which illustrates 
the plant of the Hollingsworth & Whitney Company at Water- 
ville, Maine. 



FANS. 



IQI 




Fig. 74. 



192 



STEAM-BOILERS. 







Flue to Economizer 



a" 



conomizer 



ti^= 



^-1 



1 



7\ 7\ T\ 21 



CD 



W\s.vxs^ss^^ 



Flue to Economizer 



O 



/ 




Fig. 75. 



CHIMNEYS. 193 

In this boiler room there are six horizontal multitubular 
boilers, which discharge into three circular flues running back 
over the boilers and entering one large circular flue, from 
which the gases may be passed through economizers on the way 
to the induced draught fans. In case of an accident to an econo- 
mizer the gases are put through the two economizers remaining. 
It is probable, however, that the greater part of the gas goes 
through the economizer which is nearer the fans. 

There is no by-pass around each economizer. The by-pass 
flue marked on the drawing serves the same purpose by allowing 
the gases to be sent through the other economizers. A study 
of the drawing shows that the dampers have been located with 
the above in view. 

Chimneys. — There are a number of different kinds of chim- 
neys in use to-day: the red-brick stack, the radial brick stack, 
the self-supporting steel stack, the guyed steel stack, and con- 
crete chimneys. 

The steel chimneys are sometimes lined with fire-brick and 
sometimes unlined. 

The life of a steel chimney depends upon the care taken of it; 
probably ten to twelve years is a fair estimate of the life of such a 
chimney. A steel chimney deteriorates much more rapidly when 
idle than when in use. A brick stack lasts a great many years. 

Radial brick chimneys are made of a special brick, much 
larger and thicker than the ordinary red brick, shaped to the 
curve of the chimney on two faces and radial on two faces. 

There are five or six holes about one inch square running 
vertically through these bricks. 

Radial brick chimneys are very numerous in Germany. 
Many are being built now in this country. They are known 
here as the Custodis, the Heinicke, and the Kellogg chimneys. 

Concrete reinforced by iron bars has been used for chimneys 
during the last few years. It has not always proved to be a 
success, in some cases, because of faulty design, in others, because 
of poor material and poor construction. 



194 



STEAM-BOILERS. 



Various formulae have been proposed for use in rinding the 
diameter and the height of a chimney needed for a given power, 
those given by Kent, by Christie, and by Gale being best known. 

The following table, figured by William Kent from his formula, 
is borne out by practice. The table is figured on the assumption 
that 5 pounds of coal are required per boiler horse-power. If 
less coal is required the capacity of the chimney is increased, and 

SIZES OF CHIMNEYS WITH APPROPRIATE HORSE-POWER 
OF BOILERS. 

(Kent.) 



Diam- 


Height of Chimneys and Commercial Horse-power. 


Side of 


Actual 
Area, 


eter in 
Inches. 


50 


60 


70 


80 


90 IC 





no 


125 


150 175 : 


>oo 


Spuare 
Inches. 


Square 
Feet. 


I 


eet. 


Feet 


. Feet. 


Feet. 


Feet. Fe 


St. 


Feet. 


Feet. I 


'eet. Feet. F 


eet. 






18 


23 


25 


27 


















16 


1.77 


21 


35 


38 


41 






















19 


2.41 


24 


49 


54 


58 


"62 




















22 


314 


27 


65 


72 


78 


83 




















24 


398. 


30 


84 


92 


100 


107 


113 •• 


















27 


4.91 


33 




115 


125 


133 


141 .. 


















30 


5-94 


36 




141 


15.2 


163 


173 1 


82 
















32 


7.07 


39 






183 


196 


208 2 


19 
















35 


8.30 


42 






216 


231 


245 2 


58 


271 












38 


9.62 


48 








311 


330 3 


;8 


365 


'389 








43 


12.57 


54 








363 


427 4 


49 


472 


503 




551 




48 


I5-90 


60 








505 


536 5 


65 


593 


632 




692 748 . 




54 


19.64 


66 










658 6 


u 


728 


776 




849 918 


981 


59 


2376 


72 










792 8 


$5 


876 


934 




[032 1 105 1 


181 


64 


28.27 


78 












9 


>5 


1038 


1 107 




[212 1310 1 


400 


70 


33l8 


84 












11 


6.3 


1214 


1294 




[418 1531 1 


637 


75 


38.48 


90 












... 13 


44 


1415 


1496 




[639 I770 1 


893 


80 


44.18 


96 












... 15 


37 


1616 


1720 




[876 2027 2 


167 


86 


50.27 


102 


















1946 




2133 2303 2 


462 


90 


56.75 


108 




















2192 




2402 2594 2 


773 


96 


63.62 


114 




















2459 




2687 2903 3 


003 


101 


70.88 


120 


























2990 3230 ; 


452 


106 


78.54 


126 


























3308 3573 ; 


820 


112 


86.59 


132 


























3642 3935 4 


205 


117 


95.03 


138 


























3991 431 I 4 


605 


122 


103.86 


144 


























4357 4707 5 


031 


127 


113. 10 



its new rating may be obtained by multiplying the figure given 
in the table by 5 and dividing by the actual coal used per boiler 
horse-power. 

Mr. W. W. Christie in his work on " Chimney Design " gives 
the table of chimney capacities shown on page 195. This table 
is based on 4 pounds of coal per boiler horse-power rating. 

Coal per Hour per Square Foot of Chimney Area. — It is con- 
venient in judging the capacity of a chimney to know the pounds 



CHIMNEYS. 



195 



•5 a v rt 

5. W TJ a 
cr—.x p. 



O O cm tJ- t^ O n tooo tooo rf O ■<* O 10OO mo m r^ t^oo 
m m cm cm cm ro t*3 fO to "t <t <0 100 t>» t^.00 OO O O O O m <n 








fc* 


"ft 


p, 




<u 




« 


oi 





M fe 


M 




T3 



O <U 



too m tooo w O O r^ 

o 00 t^ a n c. w 100 

M TtOO W lOO^ttOtO 

CM CM cm co co <0 "^- IOO 



OO 0> ^t "^ 0> tON N 11 
O NO 00 h\0 i- (O00 m 

N O <N to O CM O O0O00 



00 O tO to W O M lO M M lO 

N M Nlfl >00 O to CM <0 i_i 

<0O 00 M Tt W M tM/00 O >0 

H H H N N N tOtOfJ-t^ 



cm O -^-00 M M MONhM O 
On O CM O com O <0 to m O O 
O W)lON O <0O & N O CO CM 
MMMMCMCMCMCMCOtO"3-tO 



toiflH U)(> tJ-OO m Tt Tf to rf cm On 

O0 ^cm m to to OO <0 to ^ N O to 

O 00 O <n ■st'O 00 n rJ-r^O coOoo 

mmmmmCmcmcmcocO ,, ^ - '^ _ 



O O NNiONONtOrfH ^ tJ- O m HO 

O M rj- OO Tt" rJ-O OrTOOO N OnO On 

CO lOO M^h to ION O to LO00 m O0 to 

MMMMCMCMCMCMCOCOt}- 



N CM MOO OIOIOMVO M 00 f^^ 

to O ioionho to O O O coo m 

cm coco-^-ion.00 O cm TfOOO O to 

M M M M M CM CM 



CM M COCM OtOOO^M M O 
O ^00 co <N ^ O O O co m 
CM CM CM CO "vj- lOO 00 O M CO 



• OCMOO O <N O NN^t O 

• to O cm r^M m m co N cm 

. m M CM C4 CO Tf IOO N O 



00 -^" CO CM 00 NO N m 10 

O tN tooo M to 000 O O 

mmmCmcmcmco^J-O 



CMOOM^COtNtOMCMTt 

toO Om ^- n O -^-000 

M M M CM CM CM CO 



O to to n co co cm Tfco 
TfOOO O <00 OtNO 

M M M M CM CM 






00 m tJ- n O <0O O<N00 -^-00 cmoo itOO CMOO 
m cm cm cm cocococOTf'^- too O N r»00 O O O 



196 STEAM-BOILERS. 

of coal which may be taken care of per hour by each square foot 
of chimney area. 

Fig. 76 is plotted from Kent's values and from Christie's 
table of chimney sizes. 

Cost of Chimneys. — The cost of a chimney may depend 
upon its location, upon the character of the soil and other con- 
siderations, so that it is frequently the case that two chimneys 
of exactly the same dimensions differ considerably in their cost. 
The figures given below will show the range of the variation in 
price and will enable one to form a fair estimate as to the cost. 

The cost of radial brick chimneys : 

125 ft. high, 6 to 12 ft. dia. inside at top, is from $5 to $3 per rated H.P. 
150 ft. high, 8 to 14 ft. dia. inside at top, is from $4 to $2.50 per rated H.P. 
175 ft. high, 10 to 14 ft. dia. inside at top, is from $3 to $2.50 per rated H.P. 
200 ft. high, 12 ft. and over, dia. inside at top, is about $3.00 per rated H.P. 

A red brick chimney costs about 25 per cent more than a 
radial brick chimney of the same capacity; a self-supporting 
steel stack full lined, about 23 per cent more; a self-supporting 
steel stack half lined, about 14 per cent more; a self-support- 
ing steel stack unlined, about 14 per cent less; a steel stack 
guyed, about 40 per cent less than a radial brick chimney of 
the same capacity. 

Chimney Draught. — The draught produced by a chimney 
is due to the fact that the gases inside the chimney are hotter 
and consequently lighter than the outside air. Though these 
gases at a given temperature and pressure have a little greater 
specific gravity than air at the same temperature and pressure, 
the difference is not much, and may be neglected in the dis- 
cussion of chimney draught. 

To get an idea of the production of draught by a chimney, 
we may consider the conditions that would exist if a chimney 
were filled with hot air and closed at the bottom by a horizon- 
tal partition or diaphragm. The pressure of the air at the top 
of the chimney, due to the atmosphere above that level, is the 
same on the gases inside the chimney and the air outside. The 



CHIMNEYS. 



197 



































N 


,\ 


\ 






























\ 


\ 


\ 
\ 
\ 






























\ 


\ 


\ 




\ 


























\ 


\ 




\ 


























\ 


\ 


\ 


\ 


\ 


























\ 


\ 


\ 


\ 
























\ 
\ 

N 


1 




\ 
\ 


\ 


























\ 
\ 
































\ 
\ 


\ 




\ 




























\ 
\ 






\ 
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to £ 



B9ay ifanniiqo *;j *bs aod *aq jod \vo{) 



198 S TEA M -BOILERS . 

pressure on the diaphragm at the bottom is the sum of the 
pressure at the top of the chimney and of the pressure due to 
the column of hot air in the chimney. At the under side of 
the diaphragm the pressure will be that at the top of the chimney 
plus the pressure due to a column of cold air as high as the chim- 
ney. This difference of pressure is considered to be the draught, 
in all theories of the chimney. It may be readily calculated 
for an assumed set of conditions. For an actual chimney the 
draught or difference of pressure inside and outside the chimney 
may be shown by a U tube partially filled with water, and having 
one end connected to the inside of the chimney and the other 
open to the air. The water rises in the leg connected with the in- 
side of the chimney; the difference of level measures the draught. 

Suppose now that a small hole is opened in the diaphragm 
at the bottom of the chimney: cold air from without, under the 
greater pressure existing there, will enter and will force some of 
the hot air out at the top of the chimney. If the air is heated 
as it enters, to the temperature in the chimney, we shall have 
a continuous flow of cold air into and of hot air out of the chim- 
ney. Replacing the diaphragm by a grate charged with burning 
fuel, through which cold air enters and burns with the fuel, we 
have the actual conditions of chimney draught. 

The method commonly used in calculating the draught of a 
chimney, as previously stated, is to figure the difference in weight 
between a column of cold air of the same height as the chimney, 
and a column of hot air which fills the chimney. 

The temperature of the air or gases in the chimney is assumed 
to be uniform and the same as the temperature at the bottom. 

This difference in weight (which may be figured for a column 
of 1 square foot cross-section) is now divided by 62.4 and multi- 
plied by 1 2 in order to reduce to an equivalent pressure expressed 
in inches of water. 

Many of the theories proposed for calculating the dimensions 
of chimneys have started with this assumption, and many, of the 
various tables of " Chimney Draught " have been worked out 



CHIMNEYS. 



199 



240 



ll(i 



« 120- 



LOO 



in this way. During the last ten years experiments have been 
made at the Institute of Technology to determine the draught 
and the temperature at different heights in chimneys. 

A brick stack 3 by 3 feet in section and 102 feet in height 
above the grate was tapped at five 
levels for temperature and draught 
measurements. This stack, with the 
exception of 20 feet at the top, was 
entirely inside of a building heated 
to 70 . 

An unlined steel stack 3 feet in 
diameter and 100 feet in height 
above the grate was equipped with 
an iron ladder, and observations 
were taken at four landings. 

In Fig. 77 are plotted curves 
representing the result of an ex- 
tended series of observations. The 
curve A gives the variation in tem- 
perature found in the unlined steel 
stack 3 feet diameter and 100 feet 
tall. The curve B shows the varia- 
tion in temperature in a 3 by 3 foot 
square brick chimney 102 feet above 
the grate. The curves marked C 
and D represent the variation in 
temperature in a 250-foot Custodis 
chimney, 18 feet internal diameter 
at base and 16 feet internal diameter at top, located at the 
L Street Station of the Boston Edison Company. This chim- 
ney was 3 feet thick at the bottom and 8 inches at the top, 
and was taking care of about 50 pounds of coal per square foot 
of chimney area. The curve C was obtained by Messrs. Kilborn 
and Alexander, M. I. T., 191 1, and is an average of a large num- 
ber of curves. The curve marked D is a fair representation of 





1 




n 


\~ 




1 


r 


L 


Y_ 


T 


T 


T 


Hi 




1 \ 


X t 


Jvt t- 


tti-4 


+44 4 


V V^ t- 


^rV^ \ 


V Vv V 


v ^ 4v 


d\ a\ b X 


\ 



320 360 400 440 

Temperatures in Degrees Fahr. 



Fig. 77. 



200 



STEAM-BOILERS. 



another series of curves obtained from the same chimney by 
Messrs. Rhodes & Walker, M. I. T., 1912. The temperature of 
the gases entering the stack was much lower in the second series 
of tests. 

These observations of temperature were all taken by means 
of a thermal juncture which could be moved from the top to the 
bottom of the chimney and the readings taken, in 30 minutes. 

The draught was measured at the 
base of the chimney and compared 
with that figured from the average 
temperature as obtained from the 
plot. The greatest variation be- 
tween the observed draught and the 
draught as calculated was 0.09 inch 
in 1 .00 inch ; in most cases the varia- 
tion was not more than 3 per cent. 
An equation was fitted to the 
curve C of the form 

HT n = K. (See Fig. 78.) 
H = height in feet of chimney at 
any point above the middle 
of flue, the lower value of H 
being 3 feet. 

T = absolute temperature = (temperature °F. +459.5) 
n = 25 
log K = 75.4032. 



HTtK 




The mean = T av = 



area cro ss-hatched, Fig. 78 
H 2 — Hi 

r i#i 



'tW~ 



= T 



H 2 — Hi 

Example. — Assume the temperature at a level 3 feet above 
the centre of the flue as 1000 absolute, top of chimney to be 231 



CHIMNEYS. 201 

feet above the centre of the flue. Find the mean temperature 
and the probable draught when the outside air is at 3 2° F., also 
when the outside air is at 72 F. 

The specific volume of flue gas is 11.78 cubic feet, giving the 
weight of a cubic foot at 32 as 0.085 pound. 

The specific volume of air, 12.39, gives the weight of a cubic 
foot as 0.0807 pound. 



1000 X 3 /231 
25 



F-l 

— = T av = 873 



2 3!-3 

11.78 X 14-7 _ v (i4-7 ~ Q-6 X 0.04) 
49i-5 873 

v = 20.96 - = 0.0477 

V 

(0.0807 - 0-0477) (231 - 3) X 12 = i 

62.4 " 5 " 

In the preceding calculation the pressure in the chimney 
was needed; this was assumed to be (14.7 — 0.6 X 0.04), or the 
draught was assumed to be 1.20 inches at the bottom of the 
chimney. 

If the temperature of the outside air had been 72 instead of 
3 2 , the draught would have been less. In place of 0.0807 the 
figure to be used would be 

7 9 ' 5 r X O.0807 = O.O746 

(459-5 + 72) 
since the weight of a cubic foot varies at constant pressure 
inversely as the absolute temperature. 
The draught would now be : 

(0.0 7 46 - O.Q477) (231 - 3) X 12 _ iiig j nches _ 

62.4 

Draught Required. — Most boilers rated on 10 square feet of 
heating surface to a boiler horse-power are capable of develop- 



202 STEAM-BOILERS. 

ing fifty per cent more than their rated capacity on 0.5 inch 
draught at the hand damper in the uptake. 

The length of the flue between the boiler and the stack, the 
number and kinds of bends in this flue, the size of the flue, the 
resistance offered to the passage of the gases through the boiler 
itself, and the resistance offered by the grate and by the fuel bed, 
should all be considered in planning an induced draught outfit, 
or in designing a chimney. 

It is generally considered that there is a loss of draught of 
0.1 inch for each 100 feet of straight run of flue, that each sharp 
bend causes a loss of 0.05 inch, and that the resistance to the 
passage of gas through the boiler itself varies from 0.05 to 0.3 
inch. A horizontal multitubular boiler with large tubes and 

with flue area through the tubes as large as — the grate area 

7-5 
will not show a loss of over 0.05 inch when run at, or near, its 
rating. In general 0.2 to 0.3 inch is a safer amount to allow 
where the conditions are unknown. The greatest loss is in the 
passage of the air and gases through the grate and the fuel bed. 

The Stirling Boiler Company determined by experiment the 
amount of this resistance. Their results are shown by Fig. 79. 

Suppose a boiler to be located 200 feet from the stack, the 
flue having two sharp turns in it, and assume that an economizer 
is placed between the boiler and the stack. The boiler is fired 
with " run-of-mine " bituminous coal, which is burned at the 
rate of 18 pounds per square foot of grate surface per hour. From 
Fig. 79 it is seen that the resistance through the fuel bed at 18 
pounds per square foot amounts to 0.09 inch. 

The draught needed at the base of the chimney figures thus : 

Fuel bed 0.09 inch 

200-foot flue 0.20 inch 

Two sharp bends 0.10 inch 

Resistance in boiler 0.20 inch 

Resistance in economizer 0.30 inch 

Total 0.89 inch 



CHIMNEYS. 



203 




q o> 

(H3±VM iO 83H0NN M.ld H8V QNV SOVNHrtd N33MX39 C13din03a XJVbQ JO 30HOJ 



204 



STEAM-BOILERS. 



If No. i anthracite buckwheat coal were to be burned at 
the rate of 20 pounds per square foot of grate per hour, the 
draught required would be: 

Fuel bed 0.45 inch 

Flue, 200 feet 0.20 inch 

Two bends 0.10 inch 

Boiler 0.20 inch 

Economizer 0.30 inch 

Total 1.25 inch 
Where the greater part of the resistance is due to the fuel 
bed, a forced draught fan blowing air under the grate is prefer- 
able to an induced draught fan. In such cases this fan need 
deliver the air with sufficient pressure to overcome the resistance 
offered by the fuel bed only; the gas above the grate being at 
atmospheric pressure makes what is sometimes known as a bal- 
anced draught. The pull exerted by the chimney is in most 
cases sufficient to carry the gases away. 





Furnace 

Draught , 

Inches of 

Water. 


Resistance in Inches of Water 


Total Draught, 


Coal burned 

per Hour per 

Square Foot of 

Grate. 


due to 


Inches of Water. 


Passage under 

Boiler and 
through Tubes. 


Passage over 
Top of Boiler. 


With Passage 
over Top. 


Without 

Passage 

over Top. 


5 


O.04 


O.04 


O.04 


O. 12 


O.08 


8 


. II 


•05 


.04 


. 20 


.16 


IO 


•13 


.07 


•05 


•25 


. 20 


12 


■17 


.07 


•05 


.29 


.24 


14 


.19 


• IO 


•05 


•34 


•29 


15 


. 20 


. II 


•05 


•36 


•31 


16 


. 21 


. 12 


•OS 


•38 


■33 


18 


■23 


•13 


•05 


•42 


36 


20 


•24 


.16 


.06 


.46 


.40 


22 


.26 


.18 


.06 


•50 


•44 


25 


.27 


. 22 


.06 


•55 


•49 


28 


•29 


•24 


.07 


.60 


•53 


30 


■30 


.27 


.07 


.64 


•57 


34 


■32 


■31 


.08 


•7i 


•63 


36 


■33 


•34 


.08 


•75 


.67 


40 


■36 


■38 


.08 


.82 


•74 



In the Transactions of the A.S.M.E., Vol. XVII, is given the 
results of some tests conducted by J. M. Whitham to determine 



CHIMNEYS. 205 

the amount of draught needed for a certain type of boiler for 
various rates of coal consumption. 

The boiler on which the testing was done was one of 60-inch 
diameter, of the horizontal multitubular type with forty four 
4-inch tubes 20 feet long. The grate area was 26.7 square 
feet, the grates being of the herringbone type with 46 per cent 
air opening. The distance from the grate to shell was 18 inches; 
from bridge wall to shell 10 inches. The gases were returned 
over the top of the boiler. 

Areas of Chimneys and Flues. — In common practice it is 
found that satisfactory results are obtained if the area of the 
section of a chimney is made 1/10 the area of all of the grates 
connected to the chimney, where the boilers are working under 
natural draught. 

The area of a chimney used for a small plant where there is 
only one or two boilers should be made 1/8 the area of the grate. 

The flue and the uptake of a boiler are generally made 1/7 
to 1/8 the grate area. 

Forms of Chimneys. — Chimneys are made of brick or of 
steel plates. Steel chimneys are always round; large brick 
chimneys are usually round; small ones may be round or square. 
A round chimney gives a larger draught-area for the same weight 
of material, and it presents less resistance to the wind. 

Plate V gives the general arrangement and some detail of 
two chimneys: one of brick, 175 feet high, and the other of 
steel, 200 feet high. The brick chimney is built in two parts: 
the outer shell, which resists the pressure of the wind; and the 
lining, which forms the flue proper, and which may expand 
when the chimney is full of hot gases without bringing any 
stress on the shell. The shell has a foundation of rough stone 
and one course of dressed stone at the surface of the ground. 
The brickwork is splayed out inside to cover the stone foun- 
dation, and is drawn in at the top to the same diameter as the 
inside of the lining. The external form of the top is mainly 
a matter of appearance. The finish of large tiles at the top 



206 STEAM-BOILERS. 

sheds rain and keeps water from penetrating the brickwork. 
The outside of the shell has a straight taper from the base nearly 
up to the head. A system of internal buttresses, as shown in 
section at Fig. 3 and Fig. 4 (Plate V), gives the requisite stiff- 
ness to the shell without an excessive amount of material. The 
lining carries its own weight only, being protected from the wind 
by the external shell; it has a uniform diameter of 6 feet inside, 
and varies in thickness from 1 2 inches at the bottom to 4 inches 
at the top. A rectangular flue with an arched top leads into 
the chimney at one side of the foundation. 

The shell of the steel chimney is made of vertical half-inch 
plates at the base, and is splayed out to give additional bearing 
on the foundation. Above this portion the shell has a straight 
taper to the top; the plates, each 4 feet wide, vary in thickness 
from 3/8 of an inch to 1/4 of an inch. At the top an external 
finish of light plate is given for the sake of appearance. The 
foundation is of red brick, with a course of stone at the surface 
of the ground, clamped by a wrought-iron strap. The shell is 
bolted through a foundation-ring made of cast-iron segments 4 
inches thick, and a steel plate 2\ inches thick, by long bolts which 
take hold of anchor-plates bedded in the foundation. The lining 
of fire brick varies in thickness from 18 inches at the bottom to 
4I inches at the top. It lies against and is carried by the steel 
shell. The internal diameter of the chimney is intended to be 
10 feet; at places the size is a little larger on account of the 
arrangement of the lining. The lining is used to check the escape 
of heat through the steel shell. It adds nothing to the strength 
of the chimney; on the contrary, it must be carried by the shell. 
There is a chance that moisture may be harbored between the 
lining and the shell and give rise to corrosion. Large steel 
chimneys are comparatively recent, so that experience does not 
show whether lined or unlined chimneys are the more durable. 

Stability of Chimneys. — On account of the concentration 
of weight on a small area, and the disastrous results that would 
follow from defective work, the foundations of an important 



CHIMNEYS. 207 

chimney should be carefully laid by an experienced engineer. 
A natural foundation is to be preferred, but piling and other 
artificial methods of preparing the earth for the foundation 
can be used when necessary. Good natural earth should carry 
from 2000 to 4000 pounds to the square foot. The base of the 
chimney should be spread out so that this pressure, or whatever 
the earth can safely bear, may not be exceeded. 

In calculating the stability of a chimney it is customary to 
assume the maximum pressure of the wind as 55 pounds per 
square foot on a flat surface. The pressure of the wind on a 
round chimney would theoretically be two thirds of that on a 
square chimney. It is commonly assumed, however, that the 
pressure on a round chimney is 0.57 of that on a square chimney 
of the same width, on a hexagonal 0.75, and on an octagonal 
0.65. This method has long been in use, and it has been shown 
to give abundant stability. Experiments on wind-pressure are 
difficult and uncertain, and, curiously, the pressure determined 
by small gauges is commonly in excess of that shown by large 
gauges. Thus, certain experiments made during the construc- 
tion of the Forth Bridge gave a maximum wind-pressure of 
35 pounds per square foot on a large gauge 20 feet long and 
15 feet wide, while a small gauge showed a pressure of 41 pounds 
at the same time. The highest recorded pressure during violent 
gales, at the Forth Bridge, was that just quoted, namely 35 
pounds to the square foot. Small wind-gauges have shown 
a pressure of 80 to 100 pounds to the square foot; but such 
results are discredited, both because it is known that small 
gauges give too large results, and because buildings were not 
destroyed as they would have been if exposed to such wind- 
pressures. 

To determine whether a chimney is stable, treat it as a 
cantilever uniformly loaded with 55 pounds to the square foot 
and find the bending-moments and resultant stresses. The stress 
will be a tension at the windward side and a compression at 
the leeward side. Calculate the direct stress due to the weight 



208 STEAM-BOILERS. 

of the chimney, which will be a compression at either side of the 
chimney. For a brick chimney, subtract the tension due to 
wind-pressure at the windward side from the compression due 
to weight: if there is a positive remainder showing a resultant 
compression the chimney will be stable; otherwise not, because 
masonry cannot withstand tension. Again, add the compression 
due to wind-pressure to the compression due to weight, to find 
the total compression at the leeward side: if the result is not 
greater than the safe load on masonry, the chimney is strong 
enough. The safe load may be taken as 10 tons per square 
foot. 

Fig. 80 gives a graphical method of arriving at the stability 
of a chimney. At the point A, the centre of gravity of the trape- 
zoidal area against which the wind presses, a line is drawn at 
some convenient scale to represent the total wind-pressure on the 
side. From B a line BW, drawn at the same scale, represents 
the total weight of the chimney. 

Combine at point B these two forces, and if the resultant cuts 
the base at a point D, so that CD is less than 1/3 EE for 
square chimneys and less than 1/4 EE for round chimneys, 
there will be no tension on the mortar at the windward side, and 
the maximum intensity of compression will be twice the mean 
intensity. 

In the upper diagram at the right of the cut of the chimney 
the line YY represents the direct compression due to the weight 
of the chimney; the line XX the stresses due to the action 
of the wind. Combining these the line ZZ is obtained. This 
shows at the windward side a compression equal to EZ. 

The second diagram illustrates the case where the action of 
the wind just removes the compression at the windward edge, 
making EZ at the leeward edge equal to twice EY . 

The third cut shows a possible distribution of the stresses on 
a section which had cracked on the windward side. 

The calculation for the strength of a self-supporting steel 
chimney involves certain details of the design of a riveted joint 



CHIMNEYS. 



209 



and certain nice discriminations as to the action of such a joint 
when affected by a bending moment, which are out of place 
here. For example, it is clear that on the leeward side the com- 
pression on a lapped joint must be borne by the rivets and that 
the plate between the rivets is free from stress. A crude calcu- 
lation may be made as for a homogeneous cylinder, which is 




Fig. 80. 



subjected to compression and bending, using for the apparent 
working stress the safe stress of the steel, multiplied by the effi- 
ciency of the riveted joint, as determined by methods given in 
Chapter VIII. 

A calculation like that just described must be made for the 



210 



STEAM-BOILERS. 



section of the chimney at the base, for each section where there 
is a change of thickness or of construction, and for any other 
section where there is reason to suspect weakness or instability. 

A steel base built up from boiler-plate is shown by Fig. 81. 
This differs from the one shown on Plate V. 

The lining of a brick chimney is to be calculated for com- 




Fig. 81. 



pression due to weight, at the base and at each section where 

there is a reduction of thickness. The lining of a steel chimney 

must be counted in when the stress due to weight is determined. 

A separate calculation must be made for the stability of 



CHIMNEYS. 



211 



the foundation of a steel chimney. 
For this purpose find the total wind- 
pressure on the chimney and its mo- 
ment about an axis in the plane of 
the base of the foundation. Find 
also the total weight of the entire 
chimney with its lining, and of the 
foundation: this will be a vertical 
force acting through the middle of the 
foundation. Divide the moment of 
the wind-pressure by the weight of 
the chimney and foundation: the re- 
sult will be the distance from the 
middle of the foundation to the result- 
ant force due to the combined action 
of wind-pressure and weight. If this 
resultant force is inside the middle 
third of the width of the foundation, 
the chimney will be stable. 

This brief statement is intended 
to describe the method of calculating 
the stability of chimneys, and not to 
give full instructions. The design and 
calculation for an important chimney 
should be intrusted only to a compe- 
tent engineer who has had experience 
in such work. 

Radial Brick Chimneys. — This 
class of chimney is rapidly replacing 
the red brick chimney. It costs less, 
is more durable, and can be built in a 
shorter time than a red brick chimney. 

Although tall radial brick chim- 
neys are not figured to resist tension 
on the side towards the wind, the 



Air-^ 



Firebrick 




mm 



Fig. 82. 



212 



STEAM-BOILERS. 



adhesion of the mortar to the perforated radial brick is such 
that a pull of 4.4 tons per square foot is required to separate 
the joint. 

The ultimate crushing strength is about 362 tons per square 
foot. The radial bricks laid weigh about 118.5 pounds per 
cubic foot. 

It is customary in some types of radial brick chimney to 
figure 20 tons as the safe load in compression per square foot. 

In general these chimneys are not lined. There are cases, 
however, where a lining is required. The lining may be put in 
as shown in the cut of the Custodis chimney, Fig. 82. The 
weight of the fire-brick lining is carried by the shell of the 
chimney and by adding to its weight increases its stability. 



Foil moitar be 




Fig. 83. 



The method of bonding used in the Heinicke chimney is 
shown by the left-hand side of Fig. 83 ; the right-hand side shows 
how poor work might be done by an unscrupulous party if an 
inspector were not constantly on the watch. 



CHAPTER VI. 
POWER OF BOILERS. 

The power of a boiler to make steam depends on the 
amount of heat generated in the furnace, and on the propor- 
tion of that heat which is transferred to the water in the 
boiler. The amount of heat generated depends on the size 
of the grate, the rate of combustion, and the quality of the 
coal burned. The transfer of heat to the water in the boiler 
depends on the amount and arrangement of the heating-sur- 
face. In practice it is found that each type of boiler has 
certain general proportions which give good results ; any 
marked variation from these proportions is likely to give poor 
economy in the use of coal, or to lead to excessive expense in 
construction. 

The capacity of a boiler is commonly stated in boiler 
horse-power; the economy of a boiler is given in the pounds 
of steam made per pound of coal. Neither method is entirely 
satisfactory, but definite meaning is attached to the terms 
by definitions and conventions. 

Standard Fuel. — A comparison of the composition and 
of the total heats of the several kinds of coal given in the 
table on page 54 shows a great difference in the value of a 
pound of coal, depending on the district and mine from which 
it comes. In order to introduce some system into the com- 
parison of the performance of boilers in different localities it 
has been proposed that some coal or coals be selected as 
standards, and that all boiler-tests intended for comparison 
be made with a standard coal. For this purpose it has been 

213 



2 1 4 Sl^EA M -BOILERS. 

proposed to select Lehigh Valley anthracite, Pocahontas 
semi-bituminous, and Pittsburg bituminous coal. More def- 
inite comparisons would result if only one coal, such as Poca- 
hontas, were selected. The objections are, first, that some 
trouble and expense might be incurred in localities where 
this coal is not regularly on the market; and second, that 
a furnace designed for a given coal may not give its best 
results with a different kind of coal. There is a notable dif- 
ference between furnaces designed for anthracite coal and 
those designed for bituminous coal ; for the rest it appears 
that the use of a standard coal is a question merely of ex- 
pediency. 

In making a boiler-test it is not difficult to make an ap- 
proximate determination of the per cent of ash in the coal 
used. When that is done, the economy is usually stated in 
terms of water evaporated per pound of combustible, as well 
as per pound of coal. This gives somewhat more definite- 
ness to the statement ; but as no account is taken of the vola- 
tile matter in the coal, nor of the oxygen, this method also is 
indefinite. 

Value of Coal. — The actual value of a coal for making 
steam can be determined only by accurate tests with a fur- 
nace and boiler which are adapted to develop and use the 
heat that the coal can produce. While many boiler-tests 
have been made, and there is a good deal of material that 
could be used for the purpose, there has not yet been made a 
satisfactory statement of the value of the fuel in common use. 

It appears probable that the real value of a coal for mak- 
ing steam is proportional to the total heat of combustion. It 
this can be shown to be true, then coals should be sold on the 
basis of heat of combustion, just as steel is required to have 
certain physical properties which are determined by making 
proper tests. 

Quality of Steam. — When the economy of a boiler is 
stated in terms of water evaporated per pound of coal, it is 
assumed that all the water is evaporated into dry saturated 



POWER OF BOILERS. 215 

steam. But the steam which leaves the boiler may contain 
some water, or it may be superheated. 

The moisture carried along by steam is called priming. 
The steam from a properly designed boiler, working within its 
capacity, seldom carries more than three per cent of priming. 
Under favorable circumstances steam from a boiler will be 
nearly dry. 

If steam, after it passes away from the water in the boiler, 
passes over hot surfaces it will be superheated ; that is, raised 
to a temperature higher than that of saturated steam at the 
same pressure. Vertical boilers with tubes through the steam- 
space give superheated steam. If steam is to be superheated 
to any considerable extent, it must be passed through a 
superheater, either attached or independently-fired, as described 
in Chapter II. Boilers of the Manning type and boilers equipped 
with attached superheaters generally give more superheat when 
forced. This is because of the higher temperature of the escaping 
gases. 

Although the consumption of an engine, figured on pounds of 
steam, is less with superheated steam than with saturated steam, 
it does not necessarily follow that the coal per indicated horse- 
power per hour is less. A number of plants investigated by the 
writers have shown an increased coal consumption. 

Certain types of turbine must be supplied with superheated 
steam, if any economy is to be obtained, on account of the fact 
that any water in the shape of priming in the steam or any water 
resulting from the expansion of the steam acts like a water-brake. 
In some turbines it is estimated that one per cent priming causes 
two per cent loss in economy. 

Steam-space. — The steam-space and the free surface for 
the disengagement of steam should be sufficient to provide for 
the efficient separation of the steam from the water. Cylin- 
drical tubular boilers frequently have the steam-space equal to 
one third of the volume of the boiler-shell. Marine return- 
tube boilers usually have a smaller ratio of steam-space to 
water-space. 



2 1 6 STEA M -BOILERS. 

The more logical way appears to be to proportion the 
steam-space to the rate of steam-consumption by the engine. 
Thus the ratio of the volume of the steam-space of cylindri- 
cal boilers to that of the high-pressure cylinder of multiple- 
expansion engines varies from 50 : 1 to 140 : 1. The ratio of 
the steam-space of a simple locomotive-engine to the volume 
of the two cylinders is about 6J : 1. 

The capacity of the steam-space is sometimes equal to the 
volume of steam consumed by the engine in 20 seconds. It 
was found in some experiments with marine boilers having a 
working-pressure less than 50 pounds per square inch, that a 
considerable quantity of water was carried away by the steam 
when the steam-space was equal to the volume of steam con- 
sumed in 12 seconds, but that no water was carried into the 
cylinders when the steam-space was equal to the volume of 
steam used in 1 5 seconds and that no trouble from water was 
ever experienced when the steam-space was proportioned for 
20 seconds. 

All the preceding discussion refers to engines that run at a 
considerable speed of rotation — not less than 60 revolutions 
per minute. Engines that make but few revolutions per min- 
ute and take steam for only a portion of the stroke require a 
larger proportion of steam-space. As an example we may 
cite the walking-beam engines for paddle-steamers. 

Equivalent Evaporation. — The heat required to evapo- 
rate a pound of water depends on the temperature of the feed- 
water, the pressure of the steam, and the per cent of priming. 

For example, if water is supplied to a boiler at 140 F., 
and is evaporated under the pressure of 80.3 pounds by the 
gauge, with 2 per cent of priming, the heat required will be 
calculated as follows: 

The heat of the liquid at 140 F., or the heat required to 
raise a pound of water from 32 F. to that temperature, is 
108.0 B. T. U. The heat of the liquid at 95 pounds abso- 
lute, corresponding to 80.3 pounds by the gauge, is 294.6 



POWER OF BOILERS 21 7 

B. T. U. Consequently the heat required to raise the feed -water 
up to the temperature of the boiler is 

294.6-108.0=186.6 B. T. U. 

The heat of vaporization, or the heat required to change a 
pound of water into steam, at 95.0 pounds absolute, is 890.5 
B. T. U. But 2 per cent of water is found in the steam which 
comes from the boiler, leaving 98 per cent of steam; consequently 
the heat required is 

0.97x890.5=872.7 B.T. U. 

The total amount of heat is therefore 

186.6+872.7 = 1059.3 B.T. U. 

Suppose that each pound of coal evaporates 9 pounds of water, 
then the heat per pound of coal transferred to the boiler is 

9X1059.3=9534 B.T. U. 

Now the heat required to vaporize a pound of water at 212 
F., under the pressure of the atmosphere, is 969.7 B. T. U. 
Dividing the thermal units per pound of coal by this quantity 
gives 

9534-969.7=9-83, 
which is called the equivalent evaporation from and at 212 F. 

This method of stating the economy of a boiler is equivalent 
to using a special thermal unit 969.7 as large as the thermal unit 
defined on page 59. 

In making calculations involving quantities of wet steam 
it is convenient to consider the amount of steam present, 
rather than the percent of priming. In the example just con- 
sidered, there are 0.02 of water or priming, and 0.98 of steam. 
The part of a pound which is steam is represented by x. 

If the heat of vaporization at the pressure of the steam in 
the boiler is represented by r, the heat of the liquid at that 
pressure by q, and the heat of the liquid at the temperature 
of the feed-water by q ; and if, further, there are w pounds of 



2l8 STEAM-BOILERS. 

water evaporated per pound of coal, — then the equivalent 
evaporation is 

w(xr + q — g 9 ) 
969.7 

The highest equivalent evaporation per pound of coal is 
about 12 pounds, and to accomplish this result about 80 per cent 
of the total heat of combustion must be transferred to the water 
in the boiler. The complete combustion of a pound of carbon 
develops 14,650 B. T. U. ; if all this heat could be applied to 
vaporizing water at 21 2° F., then the amount of water evap- 
orated would be 

14,650 -T- 969.7 = 1 5— |— pounds. 

Few, if any, coals have a greater heat of combustion, con- 
sequently this figure may be considered to be the maximum 
equivalent evaporative power of coal. 

Should any test appear to give a larger evaporative power, 
or even a power approaching this result, it may be concluded 
either that there is an error in the test, or that there is a large 
amount of priming in the steam. Some tests of early forms 
of water-tube boilers without proper provisions for separating 
water from the steam, appeared to give extraordinary results; 
which results were due to the presence of a large amount of 
priming in the steam. At that time the methods used for 
determining the amount of priming were difficult and uncer- 
tain, and were frequently omitted in making boiler-tests. 

Boiler Horse-power — It has always been the habit to 
rate and sell boilers by the horse-power. The custom appears 
to be due to Watt, and at that time the horse-power of a 
boiler agreed very well with the power of the engine with 
which it was associated. ' The traditional method of rating 
boilers, coming down from that time, was to consider a cubic 
foot, or 62^ pounds per hour, of water evaporated into steam, 



POWER OF BOILERS. 219 

as equivalent to one boiler horse-power. This rating is now 
antiquated, and is seldom or never used. 

It was customary to consider 30 pounds of water evaporated 
per hour from a temperature of ioo° F., under the pressure of 
70 pounds by the gauge, as equivalent to one horse-power. 
This standard was recommended by a committee of the Ameri- 
can Society of Mechanical Engineers.* 

The standard now is equivalent to the vaporization of 34.5 
pounds of water per hour from and at 2 12 F. ; it is frequently 
so quoted. It is also equivalent to 33,470 B. T. U. per hour. 

Since the power from steam is developed in the engine, 
and since the economy in the use of steam depends on the 
engine only, and may vary widely with the type of engine, it 
appears illogical to assign horse-power to a boiler. The 
method appears to be justified by custom and convenience. 

Rate of Combustion. — The rate of combustion is stated 
in pounds of coal burned per square foot of grate-surface per 
hour. It varies with the draught, the kind of coal, and the 
skill of the fireman. 

In general a slow or moderate rate of combustion gj'ves 
the best results, both because the combustion is more likely 
to be complete and because the heating-surface of the boiler 
can then take up a larger portion of the heat generated. A 
very slow rate of combustion may be uneconomical, because 
there is a large excess of air admitted through the grate, and 
because there is a larger proportionate loss of heat by radia- 
tion and conduction. It is claimed that forced draught may 
be made to give complete combustion with a small amount of 
air in excess, and that it should give better economy than 
slower combustion. It will be remembered that a small 
amount of carbon monoxide due to incomplete combustion 
will cause more loss than a large amount of air in excess. 

It is true also that the harder a boiler is forced, the higher 

* Trans., vol. vi, 1881. 



220 STEAM-BOILERS. 

the temperature of the escaping gases becomes and, consequently, 
the percentage of the heat of the coal carried off in this way 
increases. 

A series of tests made by J. M. Whitham and reported in 
Trans. A.S.M.E., Vol. XVII, show that the thermal efficiency 
of a 6o-inch horizontal tubular boiler, with (44) 4-inch tubes 
20 feet long, did not change over 3 per cent between rates of 
coal consumption varying from 7 to 21 pounds per square foot 
of grate per hour. 

Heating-surface. — All the area of the shell, flues, or tubes 
of a boiler which is covered by water, and exposed to hot gases, 
is considered to be heating-surface. Any surface above the 
water-line and exposed to hot gases is counted as superheating- 
surface. The upper ends of tubes of vertical boilers are in this 
condition. 

For a cylindrical tubular boiler the heating-surface in- 
cludes all that part of the cylindrical shell which is below the 
supports at the side walls, the rear tube-plate up to the brick- 
arch which guides the gases into the tubes, and all the inside 
surface of the tubes. The front tube-plate is not counted as 
heating-surface. 

For a vertical boiler like the Manning boiler (page 11) 
the heating-surface includes the sides and crown of the fire- 
box and all the inside surface of the tubes up to the water- 
line. Surface in the tubes above the water-line is superheat- 
ing-surface. A certain 200-horse-power boiler of this type has 
1380 square feet of heating-surface and 470 square feet of super- 
heating-surface. 

The heating-surface of a locomotive-boiler consists of the 
sides and crown of the fire-box and the inside surface of the 
tubes. 

The heating-surface of a Scotch boiler consists of the surface 
of the furnace-flues above the grate and beyond the bridge, 
the inside of the combustion-chamber, and the inside surface 
of the tubes. 



POWER OF BOILERS. 221 

The effective surface of any tube-plate is the surface remain- 
ing after the areas of the openings through the tubes is deducted. 

Relative Value of Heating-surf ace. —A review of the kinds 
and conditions of heating-surface in various kinds of boilers, 
or even in a particular boiler, shows that the value of heating- 
surface varies widely. It does not appear possible to assign 
values to different kinds of heating-surface. We will note 
only that surfaces like the shell of a cylindrical boiler over the 
fire, like the inside of a fire-box, or like the flues of a marine 
boiler, which are exposed to direct radiation from the fire, are 
the most energetic in their action. Surfaces like combustion- 
chambers and tube-plates, against which the flames play, are 
nearly if not quite as good. The inside of small flues and tubes 
is less favorably situated, more especially as the flame is, under 
ordinary conditions, rapidly extinguished after it enters such 
a flue or tube. The length of the flame in small tubes depends 
on the draught, and with very strong forced draught may extend 
completely through tubes of some length. 

The value of heating-surface in a tube rapidly decreases 
with the length. It is doubtful if there is any advantage in 
making the length of a horizontal tube more than fifty times 
the diameter. Tubes of vertical boilers should have twice 
that length. 

Ordinary Proportions. — The table on the following page gives 
the ordinary proportions of various types of boilers. 

The higher rates of evaporative economy are associated with 
slower rates of combustion and with larger ratios of heating sur- 
face to grate-surface. 

No attempt is made to distinguish the kind or location of 
heating-surface; it must be understood that the ordinary ar- 
rangements and proportions for the several types are followed 
if this table is to be used in designing boilers. For example, 
it cannot be expected that heating-surface gained by length- 
ening the tubes of a locomotive-boiler will add materially to 
the efficiency of the boiler. 



222 



STEAM-BOILERS. 



Type of Boiler. 



Lancashire 

Cylindrical multitubu- 
lar 

Vertical, Manning 

Locomotive 

Locomotive type, sta- 
tionary 

Scotch marine 

Water- tube with cylin- 
der or drum 

Water-tube with sepa- 
rator 



Rate of Com- 
bustion. 



8 to 12 

8 to 15 

10 to 20 

50 to 120 

average 75 

8 to 15 
35 to 45 

9 to 15 
15 to 67 

average 20 



Square Feet 
of Heating- 
surface per 

Foot of 

Grate. 



25 to 30 

35 to 40 
*48+i6 

60 to 70 



40 to 45 
30 

35 to 45 
30 to 40 



Average 
Equivalent 
Evaporation. 



8 to IO 

9 to 10.5 
9 to 10.5 

6 . 7 to 8.5 

9 to 10.5 
7 to 9 

9 to 10.5 
7 to 9 



Square 
Feet of 

Grate 

per 
Boiler 

H.P. 



0.36 

0.30 
O.23 

O.07 



0.30 
o. 11 



O. 25 
0.22 



Heating- 
surface 

per 
Boiler 
H.P. 



7.0 

". s 

II .1 

4-5 

12.6 
3-3 

11 .0 

7-3 



* 48 heating-surface, 16 superheating-surface. 

This table has been compiled from a large number of ex- 
amples, and may be taken to represent current good practice. 
The last two columns giving the grate-surface and heating- 
surface have been computed on the basis of one horse-power 
for 34.5 pounds of water evaporated per hour from and at 

212° F. 



CHAPTER VII. 
STAYING AND OTHER DETAILS. 

ALL plates of a boiler that are not cylindrical or hemispher 
ical require staying to keep them in shape. For example, 
the cylindrical shell of a cylindrical tubular boiler does not 
require staying, because the internal pressure tends to keep it 
cylindrical. On the other hand, the pressure tends to bulge 
out the flat ends, and they must be held in place against that 
pressure. 

Many different methods of staying will be found in the 
different types of boilers seen in practice, and there are fre- 
quently several ways of staying the same kind of a surface. 
A few methods will be described in a general way. The 
placing of stays and arrangement of details is an important 
part of the design of a boiler, and must be worked out for each 
special design. 

Cylindrical Tubular Boiler. — The parts of the tube-sheets 
at the ends of a cylindrical tubular boiler, through which the 
tubes pass, are sufficiently stayed by the tubes themselves. 
The flat ends above the tubes require staying. Also, if there 
is a manhole at the bottom of the front end, the space thus 
left unsupported requires staying, and there is a corresponding 
space at the back end. 

An elaborate set of tests was made by Messrs. Yarrow* and 
Co., to determine the holding-power of tubes expanded into 
a tube-sheet. It was found that from 1 5,000 to 22,000 pounds 



* London Engineering, Jan. 6, 1893. 

223 



224 



STEAM-BOILERS. 



were required to pull out a two-inch steel tube ; in some cases 
the tube gave way by tension inside the head into which it 
was expanded. 

The staying of a flat surface consists essentially in hold- 
ing it against pressure at a series of isolated points, which are 
arranged in a regular or symmetrical pattern. A simple case 
of staying is found in the side sheets of a locomotive fire-box. 
Here the stays, which are arranged in horizontal and vertical 
rows, are screwed and riveted. If possible, the pitch or dis- 
tance between the supported points should be the same, but 
this is possible only when arranged in rows as just men- 
tioned. The allowable pitch depends on the thickness of 
the plate. For cylindrical tubular boilers the pitch of the 
supported points of the flat ends above the tubes is 3.5 to 5 
inches. The outside fibre-stress in the plate stayed may be 
from 6000 to 9000 pounds per square inch ; the calculation of 
this stress involves a knowledge of the theory of elasticity, and 
will be referred to later. 

It is not advisable, for this type of boiler, to assign a sepa- 
rate stay to each supported point of the flat surface under 
discussion, consequently the points are grouped, each point of 
the group being riveted to some support inside the boiler, 
and then the supports are held by proper stays. 

A good method of staying the flat end of a cylindrical 
boiler is shown by Plate I, and also, with some further details, 
by Fig. 84. There are two 6-inch channel-bars of proper 
length, that are riveted to the flat head. The rivets tie the 
plate to the channel-bars and thus support the plate at iso- 
lated points. The channel-bars in their turn are supported by 
stays that run directly through the boiler and have nuts and 
washers at each end. The channel-bars act as beams, and must 
be capable of carrying the load due to the pull on the rivets, 
and the through-stays must carry the loads on the beams. 
A short piece of angle-iron is riveted to the upper side of the 
upper channel-bar; it carries five additional rivets in the flat 



STAYING AND OTHER DETAILS. 225 

head, and adds an additional load to the upper cliannel-bar. 
The points where the through-stays pass through the head 
are supported directly by the stays through the washers and 
nuts. 

The lower channel-bar is a continuous girder with four spans 
and five supports. The stays form three supports and the 
other two are at the inner edge of the flange of the head. 
The upper channel-bar is a girder with three spans and foui 




FRONT HEAD FOR 60 BOILER 
84-3" TUBES 

Fig. 84. 



supports. The calculation of the stresses in the channel- 
bars is somewhat unsatisfactory, largely because the support 
at the flange of the head is uncertain; and this support must 
be left with some flexibility, and consequently with soem 
uncertainty, as too great rigidity leads to grooving. 

In arranging such a staying, we begin by determining the 
allowable pitch of the points supported by the rivets, assuming 
them to be in equidistant horizontal and vertical rows. This 
allowable pitch must not be exceeded, but the pitch may be 
made less either horizontally or vertically, or in both ways. 

A space of at least three inches is left between the top 



22 6 STEAM-BOILERS, 

row of tubes and the lowest row of jivets, and a similar space 
is left at the sides. This is to avoid grooving, 

The two upper through-stays are fifteen and a half inches 
apart on centres. They must be wide enough apart to allow 
a man to pass through. 

The stay-rods are upset at the ends so that the diameter 
at the bottom of the threads is greater than the diameter of 
the body of rod. The washer outside the plate may be 
made of copper, in which case it is made cup-shaped so as to 
bear on a narrow ring, and is made tight by calking ; or the 
washer is made of iron, and is bedded in red lead to make 
a joint. Sometimes cap-nuts are used outside the head to 
prevent the escape of steam that may leak around the screw- 
threads. Long stay-rods are sometimes supported at the 
middle. 

A method of staying otherwise similar to that just de- 
scribed, uses two angle-irons in place of a channel-bar. A 
washer of special form is used to give a proper bearing, for 
the inner nut on the through-stay, against the angle-irons. 

Fig. 85 shows a different method of staying for cylin- 
drical boilers. The left half of the figure represents the end 
elevation, and the right half represents a section through the 
manhole; this is a common method for boiler drawings. 
The supported points are arranged in sets of four, and are 
tied to forgings known as crowfeet. Fig. 86 represents such 
a crowfoot with four rivets, known as a double crowfoot; 
a single crowfoot with only two rivets is shown by Fig. 87 
When crowfeet are used they may be arranged in various 
patterns, in the example given there is a horizontal row of 
five double crowfeet just above the tubes, and three other 
double crowfeet are arranged in a circular arc. At the ends 
of the arc there are two braces like Fig. 88, which are used 
instead of single crowfeet. From each crowfoot a diagonal 
stay is carried to the boiler-shell. These stays are flattened at 
the farther end and bent to lie against the side of the shell, to 



STAYING AND OTHER DETAILS. 



227 



which they are riveted with two or three rivets ; the arrange- 
ment is similar to that of the right-hand end of the brace 




0^ 




l°\ 


._.. 


J 


r - 


J 


t ° 




--- 




Fig. 86. Fig. 87. 

shown by Fig. 88. At the crowfoot the stay has a forked 
head through which a bolt passes under the arch of the 



228 



STEAM-BOILERS. 



double crowfoot. A nut holds the bolt in place and pre 
vents the head of the stay from spreading. 




Fig. 90. 



A combination of channel-bar and crowfeet is shown by 
Fig. 80. The double crowfeet are represented as made of 
boiler-plate, bent up as shown by Fig. 90. 



STAYING AND OTHER DETAILS. 



22g 



A method of staying, suitable only for boilers which 
work under low steam-pressure, is shown by Fig. 91. Short 
pieces of T iron, arranged radially, are riveted to the head. 
Each T iron is supported from the cylindrical shell by two 




OOOOOO OOOOOO 
OOOOOO OOOOOO 

Fig. 91. 

diagonal stays; one of the stays is represented by Fig. 92. 
One end of the stay is split, and is pinned to the T iron; 
the other end is flattened, and riveted to the shell. 

The shell of a cylindrical boiler, whether it is a tubular or 
a flue boiler, is made of a series of sections or rings. Each 




Fig. 



92 



ring is made of one or two plates riveted along the edge, or 
longitudinal seam. This seam has at least two rows of rivets; 
more complicated joints are commonly used to give more 
strength to the seam. Alternate rings of the shell are made 
smaller so that they may be slipped inside the rings at each 
of their ends. The seams joining adjacent rings are com- 
monly single-riveted. The longitudinal seams are kept above 



230 STEAM-BOILERS. 

the middle of the boiler, so that they are not exposed to the fire. 
The first ring at the front end is always an outside ring, so that 
the first ring-seam has the outside edge pointing away from the 
fire; there is consequently less liability of injury to the seam 
from the flames that pass under the boiler toward the back end. 

Fig. 93 shows what is known as the Huston brace. It takes 
the place of the braces shown by Figs. 88, 90, and 92. It is made 
without welds. 

All horizontal multitubular boilers, 60 inches or over in diam- 
eter, should have a manhole in the front head, as shown by Fig. 227 
in Chapter XIII. The manhole frame is itself sufficiently stiff to 
reinforce the bottom of the front head, but the back head must 



> 



Fig, 93. 

be stayed. Ten or twelve tubes must be omitted in order to 
make room for the manhole. Fig. 94 shows a good method of 
staying the back head between the tubes and the shell. 

Two pieces of angle iron are riveted to the plate with a dis- 
tance piece or ferrule made of a piece of pipe or tube between the 
plate and the bottom of the angle irons. These ferrules hold the 
angle iron off from the plate 2 to 3 inches. 

This distance allows of a free circulation of water and pre- 
vents an overheating of the plate. A space 2 inches deep will 
be sufficiently great to prevent scale from bridging over the space 
between the angle iron and the plate. Rivets are pitched from 
5 to 8 inches along the angle irons. 

Bolts commonly made with tapering heads fitting conical 
holes in the plate pass between the angle irons and are drawn 
tight by nuts. 

Two stay-rods flattened at one end are fastened to the angle 
irons, as shown. These rods lead at a slight angle through the 



STAYING AND OTHER DETAILS. 



231 




232 STEAM-BOILERS. 

front head, one at either side of the manhole frame, and are 
fastened by nuts. The threaded ends are upset to a diameter 
greater than the centre of the rod. The angle at which the rods 
run across the boiler is so slight that there is no trouble with the 
nuts at the front head. These rods should never be tied to the 
bottom shell. Huston braces should not be used or any system 
which ties to the shell. 

Vertical Boilers. — The tube-sheets of a vertical boiler 
as is evident from inspection of Figs. 6 and 7, are usually stayed 
sufficiently by the tubes. Should the upper tube-sheet be much 
larger than the crown of the fire-box, it may need staying be- 
tween the tubes and the shell. Stays like Fig. %& may be used 
for this purpose. 

The circular fire-box of a vertical boiler is subjected to 
external pressure, and is prevented from collapsing under that 
pressure by tying it to the outer shell by screwed stay-bolts, 
which are put in and set like the stay-bolts for a locomotive- 
boiler. 

Locomotive-boiler. — The parts of a locomotive-boiler 
that require staying are the fire-box and the flat ends. The 
tube-sheets are sufficiently stayed by the tubes, but there is a 
part of the tube-sheet at the smoke-box end and a part of the 
flat end above the fire-box which requires support. The prob- 
lems here resemble those met in staying the tube-sheets of a 
horizontal cylindrical boiler, and similar methods are used. 
Thus in Plate II there are shown eight through-stays, each I-J 
of an inch in diameter. These stays pass through the girder 
staying of the crown-sheet, and have a simple nut and washer 
outside the end-plates of the boiler. At the smoke-box end, 
as shown by Figs. 1 and 3, Plate II, there are two diagonal 
stays taking hold of single crowfeet and running to the middle 
of the barrel. At the fire-box end there are four crowfeet or 
short angle-irons, made by bending up boiler plate ; two are 
shown by the right-hand elevation of Fig. 2 on Plate II. The 
outer crowfeet have five rivets, and the others six. From the 
outer crowfeet diagonal stays run to the shell at the ring just 



STAYING AND OTHER DETAILS. 233 

in front of the fire-box. From the inner crowfeet stays run to 
the middle ring of the boiler. There are also two stays like 
Fig. 88, which run to the shell above the fire-box. Finally, 
there is a crowfoot and stay at the middle of the row of eight 
through-stays, this stay fastening to the two end crown-bars. 

Below the tubes there is a place in the fire-box tube-sheet 
which requires support. This is given by three braces like 
Fig. ^S, as shown by Figs. 1 and 2, Plate II. The shell of 
the boiler, shown by this plate, is higher over the fire-box than 
it is at the barrel, and a ring of peculiar shape is required to 
join the two parts together. This ring is cylindrical below and 
conical on top ; at the sides there are flattened spaces which 
require stiffening to prevent them from springing, and thus 
start grooving of the plates. For this purpose there are three 
T irons riveted to the shell at the flattened place mentioned, 
as shown by Fig. I, Plate II. The upper ends of the T irons 
on opposite sides of the boiler are tied together by transverse 
stays above the tubes. 

Coming now to the fire-box of the boiler represented by 
Plate II, we find that at the front, rear, and sides it is tied to 
the external shell by screwed stay-bolts set in equidistant hor- 
izontal and vertical rows. The holes for these stay-bolts are 
punched or, better, drilled before the fire-box is in place. After 
it is in place and riveted to the foundation-ring a long tap is 
run through both plates, the fire-box plate and the shell, and 
thus a continuous thread is cut in the plates. A steel bolt is 
now screwed through the plates, cut to the proper length, and 
riveted cold at each end. Owing to the screw-thread on the 
bolts, this riveting is imperfect, and likely to develop cracks at 
the edge. The thread should be removed from the middle 
of the bolts, as they are then less liable to crack under the 
peculiar strains set up by the unequal expansion of the fire- 
box and outside shell. 

The stay-bolts are very likely to be cracked or broken on 
account of the expansion of the fire-box; to detect such a 



234 STEAM-BOILERS. 

failure of a bolt, or to show when excessive corrosion has taken 
place, the stay-bolts are often drilled from the outer end nearly 
through to the inner end. In case of failure steam will blow 
out of the defective stay ; serious injury has often been avoided 
by this method. 

The crown-sheet of the fire-box is exposed to intense heat, 
and is covered with only a few inches of water. The problem 
of properly staying this flat crown-sheet without interfering 
with the supply of water to it is one of the most difficult 
problems in locomotive-boiler construction. Figs. I and 2, 
Plate II, show the method of staying a crown-sheet with a sys- 
tem of girder-stays. Above the crown-sheet there are fourteen 
double girders, which are supported at the ends by castings of 
special form, shown by Figs. 2 and 6; the castings rest on the 
edges of the side sheets and on the flange of the crown-sheet* 
In addition the girder-stays are slung to the shell by sling- 
stays. At intervals of four and a half inches the crown-sheet 
is supported from the girders by bolts, having each a head in- 
side the fire-box, as shown by Fig. 5, and a nut at the top 
bearing on a plate above the girder. These plates are turned 
down at the ends to keep the two halves of the girder from 
spreading. There is a copper washer under the head of each 
bolt, inside the fire-box, to make a joint. Between the girder 
and the crown-sheet each bolt has a conical washer or thimble 
to maintain the proper distance between the girder and crown- 
sheet. This thimble is wide above to bear on the girder, and 
small below to avoid interfering with the flow of water to the 
crown-sheet, and also so as to cover as little surface as possible 
on account of the danger of burning the crown-sheet wherever 
the metal is thickened. The whole system of girders is tied 
together, and the girder nearest the fire-door is tied to the 
outside shell, thereby serving as stage for the head. It is evi- 
dent that such a system of staying is heavy, cumbersome, and 
complicated. It is also uncertain in its action, since the equal- 
ization of stresses depends on a nice adjustment of the mem- 



STAYING AND OTHER DETAILS. 



235 



bers of the system, which adjustment is liable to derangement 
from expansion of the fire-box. The girders or crown-bars are 
sometimes run lengthwise instead of transversely, but as the 
fire-box is longer than wide such an arrangement is inferior. 

To avoid the cumbersome method of staying the crown- 
sheet, which has just been described, the fire-box end of the 
boiler has been made flat on top, as shown by Fig. 95. The 




Fig. 95. 

crown-sheet can now be stayed to the outside shell by through- 
stays having nuts and copper washers at each end. The flat 
side sheets of the shell above the fire-box are also stayed by 
through-stays, and there are also three longitudinal through- 
stays in the corners of the shell over the fire-box where it 
protrudes beyond the barrel. This forms what is known as 
the Belpaire fire-box, from the inventor. 

Fig. 96 shows an attempt to combine the use of through- 
stays, like those of the Belpair fire-box, with a cylindrical top 
above the crown-sheet. It will be noted that the stays are 
neither perpendicular to the crown-sheet nor radial when they 
pierce the shell, and they must be subjected to an awkward 
side pull at both places. 

The locomotive-boiler represented by Plate III has a 
Belpair fire-box, and shows in addition some peculiarities of 



236 



STEAM-BOILERS. 



staying. Thus the flat end-plate above the fire-box has 
four T irons riveted to it. Each T iron is tied to the shell 
by two diagonal stays. Each stay has the usual double 
head at the T iron; the other end lies between, and is pinned 
to the flanges of pieces of plate that are riveted to the shell 
of the boiler. This arrangement is shown by the transverse 




and longitudinal sections through the fire-box. It will be 
noticed that the lower diagonal stays from the end-plate 
interfere with four transverse through-stays. These stays are 



STAYING AND OTHER DETAILS. 



2 37 




Sr^ 






M 



cut off and carry short vertical yokes, which are connected 
by two smaller rods, one above and one below the diagonal 
stays. 

The rings forming the barrel of the locomotive are made 
progressively smaller from the fire-box to the smoke-box; the 
slight taper toward the front end of the locomotive is found 
convenient in the design of the machine. 

Fig. 97 shows two ways of making the furnace-mouth of 
a locomotive-boiler. In one way the end- 
plate of the boiler-shell and the corre- 
sponding plate of the fire-box are flanged 
in the same direction, and are riveted out- 
side of the boiler. In the other case the 
two plates are flanged into the water-space 
and the overlapping edges are riveted. 

Jacobs-Shupert Fire-box. — This fire-box 
is made up of U-shaped sections of steel be- 
tween which are riveted stay sheets, as shown 
by Fig. 98. 

These stay sheets are perforated with 
radial slots through which the braces holding the heads pass. 

A boiler with this type of fire-box cannot be exploded through 
low water and the consequent overheating of the crown sheet. 
This was shown by tests made on June 20, 191 2, by Dr. W. 
F. M. Goss, an account of which appeared in Power, July 2d. 

Two full-sized locomotive boilers, designed for high-speed 
passenger service, were each subjected to severe low-water tests. 
Both boilers were identical in size and in design, except that one 
had a Jacobs-Shupert fire-box while the other had an ordinary 
radial stay fire-box. 

For the tests both boilers were mounted in a field some dis- 
tance apart, and were operated and observed from a bomb- 
proof hut a considerable distance away. Oil was used for fuel. 
The level of water in the boilers was read by means of a 
telescope. 



Fig. 



97- 



238 



STEAM-BOILERS. 



Each boiler was in turn run at its maximum rating, about 
1400 horse-power, and the water level allowed to drop gradually. 
The steam pressure in the Jacobs-Shupert boiler varied from 215 
to 225 pounds during the first 27 minutes, then gradually dropped 
to 50 pounds at the end of the test. The test lasted about 
55 minutes, during which time the water level dropped to more 
than 25 inches below the crown sheet. 

Examination showed that the fire-box was in good condition. 

The radial stay boiler was tested in the same manner. The 
pressure varied from 220 to 230 pounds and was 228 pounds 
at the time the boiler exploded. At the end of 23 minutes the 





.SECTION 



BACK FLUE SHEET 



Fig. 98. 



water level had fallen 14^ inches below the crown sheet when 
an explosion occurred. The crown sheet had pulled away from 
the stays. 

Marine Boiler. — The parts requiring staying in the Scotch 
boiler are the flat ends, the furnaces, and the combustion- 
chambers. The flat ends above the tubes are stayed by through- 
stays with nuts inside and with washers and nuts outside the 
plate. The boiler shown by Fig. 11, page 17, has two rows of 
through-stays — four in the upper and six in the lower row; 
two of the upper row pass through the fitting which carries the 
steam-nozzle. 

It is found in practice that the tube-sheets of a marine 



STAYING AND OTHER DETAILS. 



2 39 



boiler are not sufficiently stayed by plain tubes expanded into 
the sheets. It is customary to make a portion of the tubes 
thicker than the others, and to provide these thick tubes with 
thin nuts outside the tube-plates, so that they may act more 
effectively as stays. The thick tubes in Fig. n are indicated 
by heavy circles. Sometimes every other tube of each second 
row is made a thick tube; that is, something more than one 
fourth of the tubes are stay- tubes. Usually the number is 
fewer than this. 

Below the tubes the front plate is supported in part by 
the furnace-flues, and in part by through-stays running to the 




r~r 



4) 



U=UJ 



tgST 



^L> 



Fig. 99. 



combustion-chamber. There are two such stays above the 
furnaces and three below the furnaces in the middle of Fig. 11, 
each if inches in diameter. There are also two stays 2| inches 
in diameter, one at each side and above the furnaces. These 
last stays have one point of attachment to the front end-plate, 
but each has two points of attachment to the combustion- 
chamber. For this purpose the rear ends of the stays are 
bolted to V-shaped forgings, similar to that shown by Fig. 99. 



240 STEAM-BOILERS. 

The furnace-flues are corrugated to stiffen them, and thus 
maintain their form under the external pressure to which they 
are subjected. The corrugations in Fig. n are made up of 
alternate convex and concave semicircles; other forms of cor- 
rugations and other methods of stiffening flues, together with 
a discussion of the strength of flues, will be given in the next 
chapter. The front ends of the furnace-flues in Fig. n are 
made as large as the outside of the corrugations; the rear 
ends are as small as the inside of the corrugations. Such an 
arrangement makes it easy to remove the furnaces without 
disturbing the other parts of the boiler and without destroy- 
ing the flues. 

The combustion-chambers of a Scotch boiler are made up 
of flat or curved plates subjected to external pressure, and 
must be stayed at frequent intervals to prevent collapsing. 
The sides and bottom of the combustion-chamber in Fig. n 
are stayed to the cylindrical shell of the boiler by screwed 
stay-bolts, spaced 7 inches on centres. The back of the com- 
bustion-chamber is stayed in like manner to the back end 
of the boiler, and thus both of these flat surfaces are secured. 
The plates used for making the combustion-chamber are thicker 
than those used for a locomotive fire-box, and consequently 
the stays are spaced wider and are larger in diameter. 

The top of the combustion-chamber is stayed by stay-bolts 
and bridges in a manner that suggests the crown-bar staying 
of a locomotive fire-box. The space is, however, narrower and 
the staying is less complicated. 

Complex Stays. — Sometimes the points to be connected by 
stays are so numerous that too many through-stays will be 
required if all points are stayed separately. Thus in Fig. 99 
there is a tee-iron riveted to a flat plate, and supported at 
intervals, as indicated by the two bolts passing through it. 
Instead of using a through-stay for each bolt, the bolts are 
coupled by two V-shaped forgings, which forgings are bolted 
to a through-stay at the angle of the V. There is enough free- 



STAYING AND OTHER DETAILS. 



241 



dom of the bolts in their holes to give equal distribution of 
the pull on the through-stay. By an extension of this method 
several points may be supported by one stay-rod. 

Gusset-stays. — The flat ends of the Lancashire boiler, 
shown by Fig. 4, page 7, are secured to the cylindrical shell 
by gusset-stays; such a stay is shown more in detail by Fig. 
100. A plate is sheared to the proper form, and is riveted 




H^^ 



Fig. 100. 



between two angle-irons along the edges that come against 
the shell and the flat end. The angle-irons in turn are riveted 
to the shell or to the flat plate. Gusset-stays have the advan- 
tages of simplicity and solidity. They interfere less with the 
accessibility of the boiler than through-stays or diagonal stays. 
Their chief defect is that they are very rigid and are apt to 
localize the springing of the flat plates, which is caused by 
unequal expansion of the furnace-flues and shell. Conse- 
quently, grooving near gusset-stays is very likely to be found 
in Lancashire and Cornish boilers. Gusset-stays are also 
used to some extent in marine boilers and in locomotive- 
boilers. 

Spherical Ends. — The ends of cylindrical boilers, or of 
steam-drums, are commonly curved to form a spherical sur- 
face, in which case they retain their form under internal pres- 
sure and do not need staying. If the radius of the spherical 
surface is equal to the diameter of the cylindrical surface, the 
same thickness of plates may be used for both. If the spherical 
surface has a longer radius, the thickness may be increased. 
Such dished heads of boilers and steam-drums are struck up 



242 STEAM-BOILERS. 

between dies while at a flanging heat, and are then flanged to 
give a convenient riveting edge. 

Steam-domes are short, vertical cylinders of boiler-plate 
fastened on top of the shell of horizontal boilers. Plates II 
and III show steam-drums on locomotive-boilers. A steam- 
drum may be used to advantage when the steam-space is so 
shallow that there is danger that the ebullition may throw 
water into the pipe leading steam from the boiler. Locomo- 
tives usually have steam-domes, for not only is the steam- 
space shallow, but there is danger of splashing of the water 
in the boiler, especially if the track is rough or sharply 
curved. 

Stationary boilers ought to have steam-space enough with- 
out domes; marine boilers sometimes have domes, but they are 
less common than formerly. The additional steam-volume in 
a steam-dome is insignificant, so that a dome should not be 
added to increase steam-space of a boiler. 

The main objection to a steam-dome is that it weakens the 
boiler-shell, which must be cut away to form a junction with it. 
The shell may be reinforced, to make partial compensation, by 
a ring or flange of boiler-plate. Such a flange is clearly shown 
on Plate III, where the longitudinal seam of the ring carrying 
the dome is purposely placed at the top of the boiler. A similar 
arrangement is made for the dome on Plate II. 

Dry-pipe. — Any pipe inside of a boiler for the purpose of 
leading steam from the boiler is known as a dry-pipe; the 
pressure in such a pipe is frequently less than that of the steam 
in the boiler, consequently there is a tendency to dry the steam 
in the pipe. Dry-pipes are found in locomotive and marine 
boilers and sometimes in stationary boilers. 

The dry-pipe of a locomotive opens near the top of the 
dome. It runs vertically down till it is well below the shell of 
the barrel, then it runs horizontally through the steam-space 
and out through the smoke-box tube-sheet. The throttle-valve 
is at the inlet of the dry-pipe. It is controlled through a bell- 



STAYING AND OTHER DETAILS. 



243 



crank lever by a rod which enters the head of the boiler from 
the cab. 

The marine boiler shown by Fig. 11 has a dry-pipe which is 
joined to a steam-nozzle at the front end of the boiler. This 
dry-pipe is pierced with numerous longitudinal slits on the 
upper side; the sum of the area of such slits is seven-eighths of 
the area through the stop-valve in the steam-pipe. 

Steam-nozzle. — The stationary boiler shown on Plate I has 
a cast-iron steam-nozzle at each end. The steam-pipe leading 
steam from the boiler is bolted to the rear nozzle, and the 
safety-valves are placed above the front nozzle. 

Nozzles are often made of cast steel. The best are forged 
without welds from one piece of steel. 

Manholes. — A manhole should be large enough to allow a 
man to pass easily inside the boiler. That on Plate I is 15 
inches long and 11 inches wide, and has its greatest dimen- 
sion across the boiler. 

The manhole there shown is placed inside the shell of the boiler. 
Both the ring and the cover are forged Irom steel without a weld. 
Fig. 101 shows a form of manhole that is placed outside the shell. 




Fig. ioi. 



This form is commonly made of cast iron, but manholes of similar 
form made of steel castings are used to some extent. 

The manhole-ring should be strong enough to give compen- 
sation for the plate cut away from the ring on which it is placed. 

The manhole-cover is placed inside the ring so that it is 



244 STEAM-BOILERS. 

held up to its seat by the steam-pressure. The cover is drawn 
up to its seat by a bolt and removable yoke. Sometimes there 
are two bolts each with its yoke. A cast-iron manhole natu- 
rally has a cast-iron yoke, and a forged manhole has a wrought- 
iron or steel yoke. 

The manhole-cover is made steam-tight by a rubber gasket; 
the form of the cover and its seat are such that the gasket can- 
not be blown out by the pressure of the steam. 

Hand-holes are provided at various places on boilers to aid 
in washing out and cleaning. Thus the boiler on Plate I has a 
hand-hole near the bottom at each end, and there are several 
hand-holes near the foundation-ring of the vertical boiler, 
shown by Fig. 6. The hand-hole covers on Plate I are placed 
directly against the plate which is not reinforced. Each is 
held up by a bolt and a small yoke, which has a bearing on 
the plate completely round the hole. If the yoke has insuffi- 
cient bearing on the plate, the latter is liable to be damaged 
and leaks will occur. The hand-holes on the marine boiler 
shown by Fig. n are reinforced by small plates outside the 
boiler-heads. 

Washout Plugs. — Instead of hand-holes, washout plugs, 2 
or 2§ inches in diameter, are provided near the corners of the 
foundation-ring of a locomotive fire-box. Such plugs are simply 
screwed into the outside plate of the boiler. Examples are 
shown by Plates II and III. 

Methods of Supporting Boilers. — Horizontal cylindrical 
boilers are commonly supported on the side walls of the brick 
setting, by brackets which are riveted to the shell of the boiler. 
Thus the. boiler shown on Plate I has two such brackets on 
each side; this boiler is about 16 feet long. If a boiler is as 
much as 18 feet long, three brackets are used. The front 
brackets rest directly on the brickwork, but the other brackets 
rest on iron rollers, to provide for the expansion of the boiler. 
The brackets are set so that the plane of support is a little 
above the middle of the boiler. 



STAYING AND OTHER DETAILS. 



2 45 



Fig. 102 shows a common form of bracket, made of cast 
iron, which is riveted to the shell above the flange of the bracket. 



$x 



O O 

o 
o o 



oo 

o 

oo 



— 4-f ooo 



Fig. 102. 



Fig. 103. 



A better form with rivets both above and below the flange is 
shown by Fig. 103. 





Fig. 104. 



Fig. 105. 



A detachable bracket, like that shown by Figs. 104 and 105, 
may be used when the boiler must be put into a building through 





Fig. 106. 



Fig. 107. 

a small aperture. Fig. 104 gives an end and side elevation and 
plan of the body of the bracket; Fig. 105 gives a side elevation 



246 



STEAM-BOILERS. 



and plan, with section, of the flange. After the boiler is in place 
the flange is thrust up into the dovetail groove in the body of 
the bracket. The pressure of the flange against the dovetail 
groove, intensified by the wedging action of the inclined sides, 




Fig. 108. 




[ 



Co; 
"0" 









Fig. 109. 



/ ^*^ 



Fig. hi. 




Fig. 1 10. Fig. 112. 

is liable to be excessive. To overcome this difficulty the bracket 
shown by Figs. 106 and 107 has been used. Fig. 106 shows 
the end elevation and a view from below, of a casting which is 
riveted to the shell. Fig. 107 shows the same views of a casting 
which catches into the hollow under Fig. 106 and bears at the 



STAYIXG AND OTHER DETAILS. 



247 



top against this same casting, the rivets bolting it to the shell 
being countersunk. 

Horizontal boilers, and especially plain cylindrical boilers, 
are sometimes hung from a support above the boiler, as shown 
by Figs. 108, 109, and no. 

Fig. 108 shows a lug, made of boiler-plate, riveted to the shell 
of the boiler. The lugs are placed in pairs and the boiler is 
hung from these lugs by bolts that are supported between trans- 

& 



± 



Sid 



•ygfgiaaitsfrg 



(2) 



K3 



Fig. 113. 

verse beams over the boiler. Fig. 109 differs in substituting a 
loop for the lug. 

Fig. no shows a method of suspension with two short pieces 
of plate above the lug, to give some flexibility and provide for 
expansion. 

Figs, in and 112 show methods of suspending a boiler from 
the top. These methods are proper only for boilers which have 
a small diameter. 

Whenever possible it is better to suspend a boiler rather than 
to support it by brackets. The top of a bracket comes 3 or 4 
inches below the longitudinal joint. If, due to any settlement of 
the brickwork, the bracket bears near its outer edge, there is a 
bending moment of considerable magnitude transmitted to the 
shell. 

This tendency to pull the shell out just at the bottom of the 



248 STEAM-BOILERS. 

bracket and to push the shell in at the top of the bracket 
produces very severe strains in boilers of large diameter and 
of great weight. 

Boilers over 20 feet long require three sets of supports. 

If brackets are used it is probable that the middle set will 
either take more or less than one third the weight. 

The proper way to support such a boiler is as shown in 
Fig. 113. 

Three lugs, like Figs. 108 and 109, or preferably like Fig. 
no, are fastened to each side of the boiler. Rods from the front 
lugs pass up between two I-beams, resting on piers built up 
above the side walls of the setting, and fasten to the beams, as 
shown. 

Rods from the middle and rear lugs are attached on each side 
to an equalizer, which is in turn hung from I-beams in the same 
way as at the front. As these connections are free to turn, 
the load is always distributed in the same proportion between 
the lugs. 



CHAPTER VIII. 
STRENGTH OF BOILERS. 

The determination of the thickness of boiler-plates, the 
size of stays, and other elements affecting the strength of a 
boiler, involves a knowledge of the properties of the materials 
used and a knowledge of the methods of calculating stresses 
in the several members of the boiler. A brief statement of 
these subjects, as applied to boilers, will be given here. 

Materials Used. — The materials used for making boilers 
are mild steel, wrought iron, cast iron, malleable iron, copper, 
bronze, and brass. 

In order to insure that materials used for making a boiler 
shall have the proper qualities, it is customary to require that 
specimens shall be tested in a testing-machine, and that they 
shall have certain definite properties, such as ultimate tensile 
strength, elastic limit, and contraction of area at fracture. 
In order that these properties shall be properly developed, it 
is essential that specimens shall be of right size and shape, 
and that the testing shall proceed in a correct method. 

Testing-machines. — The frame of a testing-machine 
carries two heads, between which the test-piece is placed, and 
to which it is fastened by wedges or other clamping devices. 
One head, called the straining-head, is drawn by screws or by 
a hydraulic piston, and pulls on the test-piece. The other 
head, called the weighing-head, transmits the pull to some 
weighing device. Boiler materials are commonly tested in a 
machine which has the pull applied by screws, driven through 
gearing by hand or by power; the pull is weighed by a system 
of levers and knife-edges, arranged like those of a platform 

249 



250 STEAM-BOILERS. 

scale. Such a machine should be able to exert a pull of fifty 
or a hundred thousand pounds. 

Testing-machines that give a direct tension are commonly 
arranged to give also a direct compression. There are also 
machines arranged to give transverse loads, like the load 
applied to a beam. 

Forms of Test-pieces. — A test-piece of boiler-plate should 
be at least 1^ inches wide, planed on both edges, and should be 
about two feet long. A piece which is less than eighteen inches 
long is not fit for testing. 

Test-pieces eighteen inches to two feet long may be cut 
directly from bars or rods for making stays or bolts. If a. rod 
is so large that the available testing-machine will not break 
it, it is of course possible to turn it down to a smaller 
diameter, but it would be preferable to send such a rod to a 
machine that is powerful enough to break it at full size. 

Test-pieces of cast metal may be cast in the form of 
rectangular bars, which should be at least one inch wide and 
an inch thick. If the bars are rough or irregular it may be 
necessary to plane the edges, or perhaps to plane them all 
over. 

Test-pieces of boiler-plate should be cut from the edge 
of at least one plate of each lot of plates. Sometimes speci- 
fications require pieces from each plate used for a given boiler. 
Pieces should be cut from both the side and the end of a 
plate, for there is a grain developed by rolling either iron or 
steel boiler-plate, and tests should be made both with the 
grain and across the grain. 

Very hard material may require shoulders on the test- 
pieces to enable the testing-machine to get a proper hold. 
But iron or steel that is so hard as to require shoulders is 
much too hard for boiler-making; consequently there will be 
no reason for providing test-pieces of boiler iron or steel with 
shoulders. If test-pieces have shoulders, they should be at 
least ten inches apart. 



STRENGTH OF BOILERS. 



25 1 



Methods of Testing. 




Fig. ii4- 



-A test-piece of proper length is 
first measured to determine the 
breadth and thickness or else the 
diameter, as the case may be. 
A length of eight inches is laid 
off near the middle of the test- 
piece, and clamps for measuring 
the stretch of the piece are ap- 
plied at the ends of this eight-inch 
length, as shown by Fig. 114. 
The piece is then secured in the 
machine and a load is applied. 
The distance between the clamps 
is now measured by a micrometer 
caliper with an extension-piece. 
The method of doing this is to 
place the head of the micrometer 
against a point on the flange of 
the clamp at one end, and adjust 
the length of the micrometer so 
that it shall just touch the cor- 
responding point on the other 
clamp. A little practice will en- 
able the observer to measure to 
one or two ten-thousandths of an 
inch. As the load is increased 
the test-piece stretches, the in- 
crease of length being proportion- 
al to the increase of the load. The 
stretch is measured on both sides 
of the test-piece for each increase 
of load applied. If the test-piece 
is not straight or exactly aligned 
in the machine there may be some 
irregularity in the stretching at 



252 STEA M -BOILERS . 

first, but after a considerable load is applied the piece 
stretches uniformly until about half the maximum load that 
the piece can carry has been applied. During the progress 
of the test a point is reached beyond which the stretch in- 
creases more rapidly than the load ; this is known as the 
elastic limit. 

After the elastic limit is reached the clamps are removed 
and the test proceeds without them, but at about the same 
rate of loading. A load is soon reached which the piece 
cannot permanently endure, shown by the fact that the scale- 
beam will fall though the straining-head remains at rest. 
This is called the yield point. The piece may, however, 
carry a considerably higher load if the straining-head is kept 
moving to take up the stretch. Finally, the piece begins to 
draw down rapidly, somewhere near the middle of its length, 
and when the piece breaks, the fracture shows about half the 
area of the piece before testing. Hard materials may draw 
down little, or not at all; the limit of elasticity may approach 
the strength of the material. 

The jaws or wedges of the testing-machine interfere with 
the stretching or flow of the material gripped by them. The 
influence of the wedges may extend two or three inches 
beyond their edge in the testing of boiler-plate. If a piece 
has shoulders they will have a like effect. Consequently the 
points at which a clamp is secured to a test-piece should be 
two or three inches from a shoulder or from the wedges of the 
machine. The wedges of a machine of a capacity of fifty or 
a hundred thousand pounds are four or five inches long. 
They will grip on three inches at the end of a test-piece, but 
not on less. The test-piece must have eight inches for 
measuring stretch, two or three inches at each end for flow, 
and three to five inches at each end in the wedges. Conse- 
quently the piece must be eighteen or twenty-four inches 
long. 

The method just described is slow and laborious, and 



STRENGTH OF BOILERS. 253 

requires two observers — one to measure stretch and one to 
weigh. For commercial work an automatic device is often 
used which registers loads and corresponding elongations. 
Such devices commonly record the yield point instead of the 
elastic limit; these two points should never be confused. 

Stress. — The number of pounds of force per square inch 
is called the stress. The stress is uniform on a piece under 
direct tension, and is equal to the load divided by the area of 
transverse section. Stress may be expressed in other units, 
such as tons per square foot or kilograms per square milli- 
meter. 

Strain. — The stretch of a piece, under direct tension, per 

unit of length is called the strain. If the original length is / 

a 
and the stretch is a, then the strain is — = s. 

The Limit of Elasticity is the limiting stress beyond 
which the strain increases more rapidly than the stress. The 
limit is not perfectly definite, and can be determined approxi- 
mately only. A load greater than the elastic limit will pro- 
duce an appreciable permanent elongation after the load is 
removed. A stress less than the elastic limit will produce 
only a slight permanent elongation; such elongation may be 
inappreciable. 

Yield Point. — The stress at which the scale-beam of a 
testing-machine will fall while the straining-head is at rest is 
called the stretch limit. 

Ultimate Strength. — The maximum stress that a piece 
will endure in a testing-machine is called the ultimate strength 
of the material. The strength depends somewhat on the rate 
of testing. The more rapidly the testing proceeds the higher 
will be the apparent strength. It is desirable that some 
standard rate of testing may be adopted by engineers so that 
results may be strictly comparable. 

The Modulus of Elasticity is the result obtained by 
dividing the stress by the strain. If the stress is/ pounds 



254 STEAM-BOILERS. 

per square inch and the strain is s per inch, then the modulus 
of elasticity is 

e = £ 

s 

Reduction of Area. — The area of the test-piece of boiler- 
plate at the rupture is much less than that of the piece before 
testing. This reduction is important, as it shows the ductility 
of the metal, and its ability to change shape without too 
much distress under the influence of unequal expansion of 
different members of a boiler. 

Ultimate Elongation. — After the test-piece is broken the 
two parts are laid down in a straight line with the broken 
ends in contact, and the length of the distance between the 
points of attachments of the measuring clamps is measured. 
The ratio of the elongation to the original length (eight 
inches) is called the ultimate elongation, The ultimate elon- 
gation is generally given in per cent. This is important, for 
the same reason given for the contraction of area. 

Compression. — The preceding definitions are given for 
tension only, for sake of simplicity and brevity; they may 
be applied to pieces in direct compression if the term stretch 
or elongation is replaced by compression. 

Shearing. — Stresses have thus far been considered to be 
at right angles to the sections of the pieces to which they are 
applied, and produce either tension or compression at that 
section. A stress that is not at right angles to a section will 
tend to produce sliding at that section. A stress that is 
parallel to a section will tend to produce sliding only, and is 
called a shearing-stress. If a shearing-stress is uniformly dis- 
tributed, its intensity may be found by dividing the total force 
or load by the area of the section. 

The rivets of a riveted seam are subjected to a shearing- 
stress. 



STRENGTH OF BOILERS. 255 

Steel Specifications. — At the present time all boiler-plates 
are made of steel. 

The American standard specifications for steel of the Ameri- 
can Society of Testing Materials are universally adopted in 
the United States. That part of the specifications relating to 
boiler and rivet steel will be quoted in full. 

OPEN-HEARTH BOILER-PLATE AND RIVET STEEL. 
Adopted Aug. 16, 1909. 

Process of Manufacture. 

1. Steel shall be made by the open-hearth process. 

2. There shall be three classes of open-hearth boiler-plate 
and rivet steel; namely, flange or boiler steel, fire-box steel, and 
extra soft steel, which shall conform to the following limits in 
chemical and physical properties. 

Flange or Fire-box Extra Soft 

Boiler Steel, Steel, Steel, 

Per Cent. Per Cent. Per Cent. 

tju u l 11 * „ „„ j ( Acid 0.06 Acid 0.04 Acid 0.04 

Phosphorus shall not exceed . . . < -r, ■ ^ . ^ ^ . ^ 

^ I Basic 0.04 Basic 0.03 Basic 0.04 

Sulphur shall not exceed 0.05 0.04 0.04 

Manganese 0.30 to 0.60 0.30 to 0.50 0.30 to 0.50 

Tensile strength, lbs. per sq. in. 55,0001065,000 52,000 to 62,000 45,0001055,000 

Yield-point, in lbs. per sq. in., 

shall be not less than \ T. S. \ T. S. \ T. S. 

Elongation, per cent in 8 inches, 

shall be not less than 1,500,000 1,500,000 1,500,000 

T. S. T. S. T. S. 

(need not exceed 30%.) 

Quenchbend'. '. '. '. '. \ '. '. '. '. '. '. \ \ \ \ \ l8 °° flat *° flat ^° ^ ' 

(a) Yield- point. — For the purposes of these specifications 
the yield-point shall be determined by the careful observation of 
the drop of the beam or halt in the gauge of the testing machine. 

3. Boiler Rivet Steel. — Steel for boiler rivets shall be of the 
extra soft class as specified in paragraph 2. 

4. Modifications in Elongation for Thin and Thick Material. — 
For material less than 5/16 inch and more than 3/4 inch in 
thickness the following modifications shall be made in the re- 
quirements for elongation. 

(b) For each increase of 1/8 inch in thickness above 3/4 



256 



STEAM-BOILERS. 



inch a deduction of i shall be made from the specified percent- 
age of elongation. 

(c) For each decrease of 1/16 inch in thickness below 5/16 
inch a deduction of 2J shall be made from the specified percent- 
age of elongation. 

5. Chemical Determinations. — In order to determine if the 
material conforms to the chemical limitations prescribed in 
paragraph 2 herein, analysis shall be made by the manufacturer 
from a test ingot taken at the time of pouring of each melt of 
steel, and a correct copy of such analysis shall be furnished to 
the engineer or his inspector. A check analysis may be made by 
the purchaser or his representative from a broken tensile test- 
specimen representing each heat of flange or extra soft steel on 
an order, and for each plate as rolled of fire-box steel, in which 
cases an excess of 25 per cent above the required limits in phos- 
phorus and sulphur will be allowed. 

6. Test Specimen for Tensile Test.— The standard tensile 
test specimen of 8 inch gauged length shall be used to deter- 
mine the physical properties specified in paragraphs 2 and 3. 

The standard shape of the tensile test specimen for sheared 
plates shall be as shown in Fig. 115. 



WAtoutS^ §M (<?— Parallel Section not4ess than 9' 



it t f f • •?• 




2 



Fig. 115. 



For other material the tensile test specimen may be the 
same as for sheared plates, or it may be planed or turned parallel 
throughout its entire length, and in all cases where possible two 
opposite sides of the test specimen shall be the rolled surfaces. 

Rivet rounds and small rolled bars shall be tested of full 
size as rolled. 

7. Test Specimens for Bending Tests. — The bending test 



STRENGTH OF BOILERS. 257 

specimens shall be if inches wide if possible, and for all ma- 
terial 3/4 inch or less in thickness the test specimen shall have 
the natural rolled surface on two opposite sides; but for material 
more than 3/4 inch thick the bending test specimen may be 
1/2 inch thick. The sheared edges of bending test specimens 
shall be milled or planed. The bending test may be made by 
pressure or by blows. The cold bending test shall be made on 
the material in the condition in which it is to be used, and, prior 
to the quenched bending test, the specimen shall be heated to a 
light cherry red, as seen in the dark, and quenched in water the 
temperature of which is between 8o° and oo° F. 

Rivet rounds shall be tested of full size as rolled. 

8. Homogeneity Tests. — For fire-box steel a sample taken 
from a broken tensile test specimen shall not show any single 
seam or cavity more than one-fourth inch long in either of the 
three fractures obtained on the test for homogeneity as des- 
cribed below. 

(d) The homogeneity test is made as follows: A portion of 
the broken tensile test specimen is either nicked with a chisel or 
grooved on a machine, transversely about a sixteenth of an inch 
deep, in three places about two inches apart. The first groove 
should be made on one side, two inches from the square end of 
the specimen; the second, two inches from it on the opposite 
side; and the third, two inches from the last, and on the oppo- 
site side from it. The test specimen is then put in a vise, with 
the first groove about a quarter of an inch above the jaws, care 
being taken to hold it firmly. The projecting end of the test 
specimen is then broken off by means of a hammer, a number 
of light blows being used, and the bending being away from the 
groove. The specimen is broken at the other two grooves in the 
same way. The object of this treatment is to open and render visi- 
ble to the eye any seams due to failure to weld up, or to foreign 
interposed matter or cavities due to gas bubbles in the ingot. 
After rupture, one side of each fracture is examined, a pocket lens 
being used, if necessary, and the length of the seams and cavities 
is determined. 



258 STEAM-BOILERS. 

9. Number of Tests. — Three test pieces shall be furnished 
from each plate as it is rolled; one for tension, one for cold 
bending, and one for quench bending. For rivet rods, two ten- 
sile test specimens and two cold bending and two quench bend- 
ing test specimens shall be furnished from each melt. 

In case any one of these develops flaws, or should a tensile 
test specimen break outside of the middle third of its gauged 
length, it may be discarded and another test specimen substi- 
tuted therefor. 

10. Permissible Variation. — The variation in cross-section or 
weight of more than 2\ per cent from that specified will be 
sufficient cause for rejection, except in the case of sheared plates 
which will be covered by the following permissible variations 
which are to apply to simple plates. 

Plates when Ordered to Weight. 

(e) Plates 12^ pounds per square foot or heavier, up to 100 
inches wide, when ordered to weight, shall not average more 
than 2\ per cent variation above or 2J per cent below the theo- 
retical weight. 

(/) When 100 inches wide and over, 5 per cent above or 5 
per cent below the theoretical weight. 

(g) Plates under 12^ pounds per square foot, when ordered to 
weight, shall not average a greater variation than the following: 

Up to 75 inches wide, 2 J per cent above or 2 J per cent below 
the theoretical weight. 

(h) Seventy-five inches wide up to 100 inches wide, 5 per 
cent above or 3 per cent below the theoretical weight. 

(i) When 100 inches wide and over, 10 per cent above or 3 
per cent below the theoretical weight. 

Plates when Ordered to Gauge. 

Plates will be considered up to gauge if measuring not over 
1/100 inch less than the ordered gauge. 

An excess of weight over that corresponding to the dimen- 
sions on the order, equal in amount to that specified in the fol- 
lowing table, is allowable. 



STRENGTH OF BOILERS. 



259 



The weight of 1 cubic inch of rolled steel is assumed to be 
0.2833 pound. 

PLATES 1/4 INCH AND OVER IN THICKNESS. 



Thickness of 
Plate. Inch. 



Over 



Nominal 

Weight , 

Lbs. per Sq. Ft, 



IO. 20 
12-75 
15-3° 
I7.85 
20.40 
22.95 
25-50 



Width of Plate. 



Up to 75 Inches 
Per Cent. 



7 

6 
5 
4l 

4 

32 



75 to 100 Inches 
Per Cent. 



Over 100 Inches 
Per Cent. 



14 
12 
IO 

8 
7 

6* 
6 

5 



18 
16 

13 
10 

9 



Over 115 

Inches. 
Per Cent. 



PLATES UNDER 1/4 INCH IN THICKNESS. 


Thickness Ordered. 
Inches. 


Nominal Weight. 
Lbs. per Sq. Ft. 


Width of Plate. 


Up to 50 Inches. 
Per Cent. 


50 to 70 Inches. 
Per Cent. 


Over 70 Inches. 
Per Cent. 


1 to & 

W2 tO & 

A to! 


5. 10 to 6.37 
6.37 to 7.65 
7.65 to 10. 20 


IO 

8^ 

7 


15 

IO 


20 
17 
15 



11. Branding. — Each plate shall be distinctly stamped with 
its heat or slab number, and with the name of the manufacturer, 
grade, and lowest tensile strength specified. Each test speci- 
men shall be distinctly stamped with the heat or slab number 
which it represents. 

Rivet steel may be shipped in securely fastened bundles 
with the melt number stamped on the melt tag attached. 

12. Finish. — All finished material shall be free from in- 
jurious surface defects and laminations and must have a work- 
manlike finish. 

13. Inspection. — The inspector, representing the purchaser, 
shall have all reasonable facilities afforded to him by the manu- 
facturer to satisfy him that the finished material is furnished in 
accordance with these specifications. All tests and inspections 
shall be made at the place of manufacture prior to shipment. 

Laminations. — The upper end of the ingot into which the 
molten steel from the open-hearth furnace is cast, is liable to be 
affected by bubbles and other imperfections when the ingot is 



260 STEAM-BOILERS. 

poured from the top. Such imperfections, if they are not re- 
moved, give rise to lamination in the plates, and therefore when 
the ingot is rolled into blooms the crop end should be cut long 
enough to remove all the bubbles. 

Blue Heat. — Steel plates, and other forms of mild steel, 
become brittle at a temperature corresponding, roughly, to a 
blue heat. A plate that will endure bending double, both 
hot and cold, is liable to show cracks if bent at a blue heat. 
In bending, flanging, and forging no work should be done on 
steel at a blue heat; properly, such work should be done at 
a bright red heat; work should never be continued after the 
steel becomes black. After the steel is cold it may be bent 
as readily as iron at the same temperature. 

Wrought Iron. — All the stays and fastenings of boilers 
that are made by welding should be made of tough, ductile 
wrought iron. Welds made by a skilful smith may have as 
great a strength as the bar from which they are made. A 
ductile bar may break in the clear bar instead of in the weld, 
on account of the hardening due to the work done on the bar 
at the weld. It is customary to assume that 25 to 50 per 
cent of the strength of the bar may be lost by welding. 

Wrought-iron plates of a quality suitable for boiler-making 
are now more expensive than mild-steel plates, which are in 
every way as well adapted to the purpose, and which have a 
higher strength. Consequently we find wrought-iron plates 
used only when specially demanded. Wrought iron does not 
show cracks when worked at a blue heat, and in general may 
endure more abuse in working. This caused wrought iron 
to be preferred by many after reliable steel was produced 
cheaply, but boiler-makers now understand the working of 
steel plates and avoid improper handling. 

Wrought-iron plates should show a limit of elasticity of 
23,000 pounds, and a tensile strength of 45,000 pounds to 
the square inch. 



STRENGTH OF BOILERS. 2 fa 

Wrought-iron rods and bolts should have a strength of 
48,000 pounds per square inch. 

Rivets. — The rivets used in boiler-making are either iron, 
or steel similar in quality to steel used for boiler-plates. 

A rivet should bend cold around a bar of the same 
diameter, and it should bend double when hot without frac- 
ture. The tail should admit of being hammered down when 
hot till it forms a disk 2\ times the diameter of the shank, 
without cracking. The shank should admit of being ham- 
mered flat when cold, and then punched with a hole equal in 
diameter to that of the shank, without cracking. 

The rods from which rivets are made should show a tensile 
strength of about 55,000 pounds for steel and about 48,000 
pounds for wrought iron. The other properties, such as 
ultimate elongation and contraction of area, should be like 
those for boiler-plate. 

The shearing strength of steel rivets is about 45,000 
pounds, and of iron rivets about 38,000 pounds; that is, the 
shearing strength will be between T 7 o and T 8 o of the tensile 
strength. 

Cast Iron in different forms will show a tensile strength 
of 16,000 to 24,000 pounds to the square inch. Gun-iron, 
which is cast iron made with special care and skill from 
selected stock, has shown a tensile strength of nearly 30,000 
pounds to the square inch. In compression the strength of 
small pieces may be as high as 80,000 pounds to the square 
inch, but larger pieces, like columns, fail at 30,000 pounds 
to the square inch. 

Cast iron is used for some or all of the parts of sectional 
boilers, and for fittings such as manholes, though wrought 
iron is preferable for such purposes. Flat plates at the ends 
of cylindrical boilers are sometimes made of cast iron. 

In general, cast iron should never be used when it is sub- 
jected to severe changes of temperature or to stresses from 



2 62 STEAM-BOILERS. 

unequal expansion, and should be replaced by wrought iron 
or mild steel whenever it is practicable. 

Couplings, elbows, and other pipe-fittings are made of 
cast iron. The brittleness is a convenience when changes are 
to be made, as joints that cannot be opened are readily 
broken. 

Malleable Iron, which is cast iron toughened by being 
deprived of part of the carbon, is used for pipe-fittings and for 
fittings of steam-boilers. It is used in place of cast iron for 
sectional boilers and for parts of water-tube boilers. Though 
tougher than cast iron, and though it will endure forging to 
some extent, its variability in quality and its unreliability 
prevent much reduction in weight and size when substituted 
for cast iron. 

Copper is largely used in Europe for making fire-boxes of 
locomotive-boilers and torpedo-boat boilers. Its greater cost 
is in part offset by the value of the scrap copper after the 
fire-box is worn out. 

Copper for fire-boxes, rivets, and stays should have a ten- 
sile strength of 34,000 pounds to the square inch, and should 
show an elongation of 20 to 25 per cent in 8 inches. It should 
not contain more than one-half per cent of impurities. The 
greater ductility of copper, and its greater thermal conduc- 
tivity, permitting of greater thickness for furnace-plates, 
recommends it to European engineers. 

Copper is largely used on steamships for making piping of 
all sorts, such as steam-pipes and water-pipes. Such pipes 
are made of sheet copper, rolled up or hammered to shape, 
scarfed and brazed at the edges. The pipe is also brazed to 
brass flanges for coupling lengths of pipe, or for joining to 
steam-chests or other parts of the engine or boiler. If the 
brazing is not done with care and skill the brazed joint may 
lose as much as half the strength of the sheet copper. . Several 
disastrous explosions of such piping have occurred. Conse- 



STRENGTH OF BOILERS. 263 

quently wrought-iron piping is finding favor for high-pressure 
steam. 

Bronze and Composition. Brass. — Bronze is properly 
an alloy of copper and tin; thus gun-metal is 90 parts of 
copper to 10 of tin. Compositions of various qualities are 
made of copper and zinc with more or less tin. Brass is an 
alloy of copper and zinc; for example, brass smoke-tubes are 
made of 70 parts of copper to 30 parts of zinc. Lead is 
added to brass and to composition to reduce the cost and to 
make the metal work easier. It may be considered as an 
adulteration, as it cheapens the metal at the expense of the 
quality. There are many special bronzes, such as phosphor- 
bronze and aluminium-bronze, which are used for special 
purposes. 

Brass is used to some extent for smoke-tubes of locomo- 
tive and other boilers, on account of its greater thermal con- 
ductivity, by European engineers. In America, brass is used 
for valves, gauges, and other boiler fittings. Composition or 
bronze is advantageously used for the valves and seats of 
safety-valves and wherever the service endured is excep- 
tionally hard. Brass is more commonly used because it is 
cheaper. In a general way it may be said that the cost and 
quality of brass and composition is proportional to the copper 
it contains; thus red brass is better and costs more than 
yellow brass. Many small brass fittings on the market are 
sold at a price which precludes the use of proper alloys, and 
they are consequently soft and worthless. 

Stay-bolts are usually arranged in equidistant horizontal 
and vertical rows; as an example we may take the stay-bolts 
in the locomotive fire-box on Plate II. These bolts are 7/8 
of an inch in diameter outside of the threads, and are spaced 
4 inches on centres. The total load on each stay-bolt with 
a steam-pressure of 170 pounds to the square inch is 

4 X 4 X 170 = 2720 pounds. 



26a steam-boilers. 

The diameter of the bolt at the bottom of the screw-thread 
is about 0.7 of an inch, and the area of the section is about 
0.4 of a square inch. The stress is consequently 

2720 -^ 0.4 = 6800. 

Sometimes the area is calculated from the external diam- 
eter of the bolt, a proceeding which may lead to a gross error. 
In the present instance the corresponding area is about 0.6 
of a square inch, which gives an apparent stress of about 
4500. 

Suppose that the thread is turned off from the body of 
the bolt, and that the diameter is thereby reduced to 5/8 of 
an inch. The area of the section is then about 0.3 of an 
inch, and the stress is 

2720 -f- 0.3 = 9000 +• 

The stress on stay-bolts should always be low to allow 
for wasting from corrosion, and to allow for unknown addi- 
tional stresses that may be caused by the unequal expansion 
of the plates that are tied together by the stay-bolts. 

Stay-rods. — Through-stays like those passing through the 
steam-space of the marine boiler, shown by Fig. 11, page 17, 
are treated much like stay-bolts. Thus the stays in question 
are 14 inches apart horizontally and 13 inches apart vertically. 
If they are each assumed to support a rectangular area 13 
inches wide and 14 inches long, the total force from 160 
pounds steam-pressure will be 

14 X 13 X 160 = 29120. 

The diameter of these stays in the body is 2 inches, which 
gives an area of section of 3.14 square inches. The stress is 
consequently 

29120 -T- 3. 14 = 9300 



STRENGTH OF BOILERS. 



265 



These stay-rods have swaged heads on which the screw- 
thread is cut, so that the diameter at the bottom of the 
thread is greater than the diameter of the body. 

Stay-rods which are used in connection with girders, as on 
Plate I, will have to carry loads which depend on the surface 
supported, the steam-pressure, and the number and arrange- 
ment of the stays. The determination of the load may be 
difficult and uncertain, but the calculation of the stress for a 
given load is very simple. 

Diagonal Stays. — If a stay-rod runs diagonally from a 
flat plate to the shell of a boiler, it will evidently be subjected 
e - / 




Fig. 116. 
to a greater stress than it would be if it were a through-stay. 
Thus in Fig. 116 we have at the point a the parallelogram of 
forces abcd\ ab is the total pressure supported by the stay, ac 
is the pull on the stay, and ad is a force that must be taken 
up by the flat plate. But the triangles abc and aef are simi- 
lar, so that we have 



ac 

ab 



ef 



*« + Tf 



'/ 



Suppose, for example, that ae is two feet and ef is six 
feet; then 



ab ~ 6 



= 1.054, 




266 STEAM-BOILERS. 

or the pull on the stay is more than five per cent in excess of 
what a through-stay would be required to support. 

Gusset-stays are open to the defect that the distribu- 
tion of stress on the plate forming the stay is uneven and 
uncertain. It is customary to calculate them on the assump- 
tion that the resultant stress acts along 
a medial line, and is evenly distributed 
over a section at right angles to that line. 
A low apparent working-stress should be 
used. \ / 

Thin Hollow Cylinder. — Let Fig. 

117 represent a semicircular steam-drum ^-~ --" 

closed at the bottom by a thick flat plate. FlG< " 7 - 

If the steam-pressure is/ pounds per square inch, the radius 

is r, and the length is /, then the pressure on the plate is 

2prl. 

If the thickness of the cylinder is /, and the stress per 
square inch on the metal of the cylinder is s, then the pull of 
the cylinder at one end of the plate is 

stl. 

But this must be equal to half the pressure on the plate, 
so that 

stl = prl. 

.,.-£ 

For safety the stress should not exceed the safe working 
stress for the material of which the cylinder is made ; so that 
we have 

/-* 



STRENGTH OF BOILERS. 267 

It is evident that the pull on the side of the cylinder and 
the stress per square inch will be the same if another half- 
cylinder is substituted for this plate, making a complete thin 
hollow cylinder. 

Example 1. — A thin hollow cylinder five feet in diameter 
and half an inch thick, working at a pressure of 200 pounds, 
will be subjected to a stress of 

5 X 12 
200 X r- i = 12,000 

pounds per square inch. If the cylinder is made of one con- 
tinuous plate of steel without longitudinal joint, this stress 
will be about one fifth of the ultimate strength. 

Example 2. — If it is desired that the stress shall be 9000 
pounds in a cylinder 9 feet in diameter when exposed to a 
pressure of 120 pounds to the square inch, then the thickness 
of the plate should be 

pr 9 X 12 
t = ~ = 120 X -f- 9000 = 0.72 

of an inch. 

End Tension on a Cylinder. — In the preceding cylinder 
we have considered the tension on a section at the side of the 
cylinder. Let us now consider the tension on a transverse 
section. 

If the cylinder is closed by a flat plate at the end, the 
area of that plate will be 

3.1416V, 

and the total force due to a pressure of p pounds per square 
inch will be 

3.1416^. 



268 STEAM-BOILERS. 

This force will be resisted by a ring of metal having a cir- 
cumference 2 X 3.1416?-, and a thickness t. The resistance 
of the ring will be 

2 X 3.i4i°>/j, 

representing the stress by s. Consequently we shall have 

2 X 3.i4i6rAy = 3.1416^/. 

pr 
•'• s = 2t' 

It is evident that the stress from the end pull is half the 
stress on the section at the side of a cylinder, and conse- 
quently a cylinder made of homogeneous material without 
joints will always be ruptured longitudinally. 

It is also evident that the stress from the end pull will be 
the same if the end of the cylinder is closed by a spherical 
surface, or by any other figure, instead of a flat plate. 

Thin Hollow Sphere- — A section taken through the cen- 
tre of a sphere is in the same condition as a transverse sec- 
tion of a thin cylinder, and will be subjected to the same 
stress, if the sphere has the same thickness and is subjected 
to the same internal pressure. 

Formerly the ends of plain cylindrical boilers were made 
hemispherical, but such ends are difficult to make and are 
needlessly strong if of the same thickness as the cylindrical 
shell. It is now the practice to curve such ends to a less 
radius than that of the cylindrical shell. If the radius of the 
head is equal to the diameter of the shell, then with the same 
thickness of plate the stress will be the same per square inch, 
provided there are no seams in head or shell. The heads 
usually do not have a seam, and the shells always have a 
seam; the margin of strength in the head, when the same 
thickness of plate is used, under this condition may be offset 
against the possible injury done to the head in shaping it. 



STRENGTH OF BOILERS. 



269 



The construction known as a bumped-np head has the 
edge flanged into a cylindrical form to make a joint with the 
shell, and to avoid the awkward stress that would be thrown 
onto the cylindrical shell if the true cylindrical and spherical 
surfaces were allowed to intersect. 

If it is inconvenient to curve the head to a radius as small 
as the diameter of the cylinder, then a thicker 
plate may be used, with a longer radius. 

Rivets. — The plates of a boiler are joined at 
the edges by rivets; rivets are also used in stays 
and other members. 

The usual form of rivets is shown by Fig. 
118. If the diameter of the rivet is D> then the 
proportions may be 



g3[ 




A 
D 



■4; 



R 
D 



— 1.2 



C 
D 



0.7 



D 



= 3/4. 



The length of the rivet will depend on the number and 
thickness of the plates through which it is to pass. 

The rivet represented by Fig. 118 has a pan head. Of the 
rivets shown by Fig. 119, A, B, and C have pan heads, and D 
and E have round or hemispherical heads. 

The form of the point of a rivet will depend on the way 
in which the rivet is driven and on the shape of the tools or 
dies used for forming the point. The rivet A has a straight 



270 



STEAM-BOILERS. 



conical point ; this is the only form that can be made when 
the rivet is driven by hand with flat-faced hammers. 

The rivet B has the head formed by a die or snap. The 
rivet is driven by a few heavy blows of a hammer, and the 
head is roughly formed ; then a die or snap is placed on the 
point and driven to form the point by a sledge-hammer. 

C shows a rounded conical point commonly used for 
machine-driven rivets. The heads of such rivets may have a 
similar form. 

D represents the usual form of countersunk rivets: the 
hemispherical head is not a peculiarity of such rivets; it is 




Fig. 



119. 



occasionally used with any form of point. The rivet E has 
some fulness or projection at the point beyond the counter- 
sink. 

After a rivet is driven, both ends are called heads; the 
distinction of heads and points is made here for convenience 
in description. 

The straight conical form A is liable to be too flat and 
weak. Its height should be three-fourths the diameter of 
the rivet. 

When rivet-holes are punched in plates they are slightly 
conical, as shown by B,Fig. 119, which shows the two smaller 
ends of the rivet-holes placed together to facilitate the proper 
filling of the hole by the rivets. The other rivet-holes are 
straight, as they would be if drilled. 



STRENGTH OF BOILERS. 271 

Riveted Joints. — The proportions of riveted joints, such 
as diameter and pitch of rivets, are determined in part by 
practice and in part by a method of calculation to be explained 
later. In practice it is found necessary to limit the pitch of 
the rivets, and consequently the diameter, to be used w.ith a 
given thickness of plate, in order that the joint may be made 
tight by calking. This limitation frequently makes the joint 
weaker than it otherwise would be. 

The edges of plates are either lapped over and rivetec 1 , or 
brought edge to edge and then joined by a cover-plate which 
is riveted to each of the two plates. The first method makes 
a lap-joint and the second a butt-joint. 

Fig. 120 shows a single-riveted lap-joint and Figs. 121 and 
122 show double-riveted lap-joints. The rivets in Fig. 121 are 
said to be staggered; the form shown by Fig. 122 is called chain- 
riveting. 

Butt-joints with two cover-plates are shown by Figs. 125, 
126, and 127. The outer cover-plate is narrow, with rivets 
placed close enough together to provide for sound calking. 
The inner plate is wider, and as its edges are not calked they 
may have a row of more widely spaced rivets. These joints, and 
those shown by Figs. 123 and 124, are designed with the view of 
securing more strength than can be had with a plain lap-joint 
like Fig. 121, or than can be had with a butt-joint with cover- 
plates of equal width. 

Efficiency of a Riveted Joint. — The strength of a riveted 
joint is always less than that of the solid plate, because some of 
the plate is cut away by the rivets. This is very evident in the 
case of a single-riveted joint, such as that shown by Fig. 120. It 
will be found to be true for more complicated joints, such as 
those shown by Figs. 125, 126, and 127. The efficiency of a 
riveted joint is the ratio of the strength of the joint to the 
strength of the solid plate. 

The strength and efficiency of a given riveted joint can be 



272 STEAM-BOILERS. 

properly determined only by direct test on full-sized speci- 
mens, which have considerable width. Tests on narrow 
specimens are liable to be misleading. Tests on boiler-joints 
are expensive, and can be made only on large and power- 
ful testing-machines. Tests have been made on behalf of 
the United States Navy Department at the Watertown 
Arsenal on a large number of single-riveted joints, on a con- 
siderable number of double-riveted joints, and on a few 
special joints. A few tests have been made elsewhere on full- 
sized joints. These tests give us important information that 
can be used in designing joints for boilers, but we cannot in 
general select a joint directly from the tests. 

Methods of Failure. — A riveted joint may fail in one of 
several methods, depending on the proportions, such as thick- 
ness of plate and the diameter and pitch of the rivets. This 
can be clearly seen in case of a single-riveted joint like that 
shown by Fig. 120. Such a joint may fail: 

(1) By tearing the plate at the reduced section between the 
rivets. If the rivets have the diameter d and the pitch /, 
then the ratio of the area of the reduced section to that of 
the whole plate is 

i> — d 



P 



(2) By shearing the rivets. 

(3) By crushing the plate or the rivets at the surface where 
they are in contact. 

(4) By cracking the plate between the rivet-hole and the 
edge of the plate, or by some method of failure due to in- 
sufficient lap. A riveted joint never fails by this method in 
practice, because the lap can always be made sufficient. 

The failure of more complicated joints may occur in 
various methods, which will be considered In connection with 
the calculation of some special joints. 



STRENGTH OF BOILERS. 273 

Drilled or Punched Plates. — In the better class of boiler- 
shops it is now the practice to drill rivet-holes in plates after 
the plates are in place, so that the holes are sure to be fair. 
Sometimes the holes are punched to a smaller diameter and 
then drilled out to the final size after the plates are in place. 
The result is the same as though the holes were drilled in the 
first place, as the metal near the hole, which was injured in 
punching, is all removed. The metal remaining between 
drilled holes does not have its properties changed by the 
drilling. On the contrary, the metal between punched holes 
is always injured more or less. In general, soft ductile metal 
is injured less than hard metal, and further, soft-steel plates 
are injured less than wrought-iron plates. 

When boiler-plates are punched and then rolled to form 
cylindrical shells, some of the holes are liable to come unfair, 
so that a rivet cannot be passed through. In such cases the 
holes should be drilled to a larger size, and a rivet of corre- 
sponding diameter should be substituted. Careless or reck- 
less workmen sometimes drive in a drift-pin, and stretch or 
distort the unfair holes so that a rivet can be forced through. 
The plate is liable to be severely injured by such treatment, 
and the rivet cannot properly fill the rivet-holes. Unfortu- 
nately it is difficult or impossible to detect bad work of this 
kind after the rivets are driven. 

Tearing. — The metal between the rivet-holes in a riveted 
joint cannot stretch as a proper test-piece does in the testing- 
machine, and consequently it shows a greater tensile strength 
than a test-piece from the same plate. Some tests on single 
or double riveted joints with small pitches show an excess 
of strength from this cause, amounting to ten per cent or 
more. The excess appears to be uncertain and irregular, so 
that if any allowance is made for it, it should be by a skilled 
designer after a careful study of all the tests that have been 
made. Ordinarily it will be safer to use the tensile strength 
shown by test-pieces in the testing-machine, especially for joints 
like Fig. 12.-2, which have a large pitch for some of the rivets. 



274 STEAM-BOILERS. 

Shearing". — In general it is fair to assume the shearing 
strength of rivets of iron or steel to be between T V and T % of the 
tensile strength of the metal from which the rivets are made. 

Crushing. — It is customary to assume that the pull on a 
riveted joint is evenly distributed among the rivets in the 
joint, and to divide the total pull by the number of rivets to 
find the shearing or crushing force acting on one rivet. It is 
further customary to assume that the intensity of the crushing 
force on the surface where the rivet bears on the plate, may 
be found by dividing the total force on one rivet, by the 
product of the diameter of a rivet and the thickness of the 
plate. 

The crushing-stress on rivets in joints that fail by crushing 
is found by experiment to be high and irregular. In some 
cases it has amounted to 150,000 pounds per square inch; in 
a few tests it is less than 85,000 pounds. It is probable that 
95,000 pounds may be used with safety in calculating riveted 
joints for boilers. Now the stress on the bearing-surface 
will seldom be so much as one third the ultimate strength, 
even during a hydraulic test of a boiler, and it is not probable 
that a joint will be injured in this way unless the stress 
approaches the ultimate strength. 

Friction of Riveted Joints. — It is evident that there must 
be considerable friction between plates that are firmly clamped 
together by rivets driven hot. It has been proposed to take 
some account of this friction in calculating riveted joints, or 
even to allow the friction to be the determining element in 
proportioning riveted joints. Such a method is shown by 
experiment to be unsafe, for slipping takes place at all loads, 
beginning at loads that are much smaller than a safe load, and 
the effect of friction disappears before a breaking load is 
reached. 

Lap. — The distance from the centre of the rivet-hole to 
the edge of the plate is called the lap. The lap is usually 
once and a half the diameter of the rivet, a proportion that 
appears to be satisfactory. 



STRENGTH OF BOILERS. 



275 



Diameter of Rivet. — The minimum diameter of punched 
holes is determined by the consideration that the punch 
should not be broken. In the ordinary methods of punching 
boiler-plates the diameter of the punch should at least be as 
much as the thickness of the plate. It very commonly is 
once and a half the thickness of the plate. 

Drilled rivet-holes may have any diameter. They never 
have a diameter less than the thickness of the plate. The 
maximum diameter of rivet to be used with any kind of 
riveted joint will in general be determined by the considera- 
tion that the tendency to crush the plate in front of the rivet 
should not be greater than the shearing strength of the rivet. 
The maximum diameter thus found is liable to give too large 
a pitch. 

Pitch.— The maximum pitch for a given plate along a 
calked edge should be determined by the consideration that 
the plate should be held up rigidly enough to make a tight 
joint without excessive calking. The pitch of rivets, like 
those in the outer row of the joint shown by Fig. 127, need 
not be governed by this rule. There does not appear to be 
any explicit rule deduced either from practice or experiment 
for determining the proper pitch of rivets. 

Single-riveted Lap-joint. — In the joint shown by Fig. 120 
let the thickness of the plate be t, the 
diameter of the rivet d, and the pitch 
p y all in inches. Let the tearing 
strength of the plate be f t — 55,000, 
the shearing strength be f s = 45,000, 
and the resistance to crushing be 
ft — 95> 000 > a ^ f° r milci steel. 
Assume the proportions 

Fig. 120. ^=15/16, t = y/\6, p — 2\. 

It will be sufficient to consider a portion of the plate 
having a width equal to the pitch. The failure of such a strip 
may occur in one of three ways: 



.1 



2j6 STEAM-BOILERS. 

72 

ist. Shearing one rivet. The area to be sheared is — 

x lAldd* 

or — . The resistance to shearing is found by multi- 

4 

plying this area by the shearing strength of the rivet : 
nd % x n X 15 X 15 X 45, 000 

T" /s = 4X163T16- = 3I '° 63 ' 

2d. Tearing plate between rivets. The effective width of 
the strip under consideration, allowing for the rivet-hole, is 
p — d, and the thickness of the plate is t ; the resistance to 
tearing is 

{p - d)tf t = (2}.- f£) T V X 55,ooo = 31,580. 

3d. Crushing of rivet or plate. The conventional method 
is to assume the effective bearing area to be equivalent to the 
diameter of the rivet multiplied by the thickness of the plate. 
The resistance is considered to be 

dt fc = H X T \ X 95,000 = 38,970. 

The strength of a strip of the plate 2\ inches wide is 

2 i X T 7 6 X 55,ooo= 54, HO. 

The calculated resistance to shearing is less than the 
resistance to tearing or compression. The apparent effi- 
ciency of the joint is 

31,063 

100 X = 57-4 P er cent - 

^ 54,140 

If it De assumed that the resistance to tearing of the 
section between rivets will have an excess of ten per cent 
over the resistance of a piece in a testing-machine, then the 
resistance to tearing between rivets will appear to be 34,740 
This figure is not far from the resistance to shearing, though 
still inferior. If it be further assumed that the whole plate 



STRENGTH OF BOILERS. 



277 



outside of the joint will show a tearing strength of only 
55,000 pounds per square inch, the efficiency of the joint will 
appear to be more than five per cent greater than that given 
above. It is probably wise to ignore the excess of strength 
due to the fact that the plate between the rivets will not 
draw down for reasons that have already been stated at length. 
Double-riveted Lap-joint. — The rivets in this joint may 
be staggered as shown by Fig. 121, or chain-riveting may be 





Fig. 121. 



used as in Fig. 122. If the rivets are staggered and the two 
rows are too near together, it is possible that the plate may 




Fig. 122. 



tear down from a rivet in one row to the nearest rivet in the 
next row, and thus have, after tearing, a jagged edge. With 
the usual proportions such a failure will not occur, but the 
plate will tear between rivets in the same row, if it fails by 



278 STEAM-BOILERS. 

tearing. The calculation for efficiency will consequently be 
the same for both methods of riveting. 

Let the dimensions be 

t = ;/i6, d = 13/16, / = 2j. 

The joint may fail in one of three ways: 

1st. Shearing two rivets. The assumed strip having a 

width equal to the pitch will be held by two rivets ; this is 

apparent at once for chain-riveting. For staggered rivets 

such a strip will contain one whole rivet and half of two 

others, so that the same rule holds. The resistance of two 

rivets to shearing will be 

2nd 2 . - ^ 

■ f g = 46,660. 

4 
2d. Tearing between two rivets. The resistance is 

{p — d)tf t = 40,600 

3d. Crushing in front of rivets. Just as for shearing, we 
have here the resistance at two rivets equal to 

2dtf= 67,540. 

The strength of the plate for a width of the pitch is 

ptf = 60,160. 

The plate will apparently fail by tearing, and the effi- 
ciency of the joint will be 

40,600 ^ 
100 X 7 ^ - = 67.5 per cent. 
60,160 

The increase of efficiency of the double-riveted lap-joint 
over the single-riveted joint is clearly due to reducing the 
diameter of the rivet and increasing the pitch. A further 
increase of efficiency could be obtained by using three rows of 
rivets ; this, however, is practicable only for thick plates, as 
we are liable to get too wide a pitch for sound calking. 

Single-riveted Lap-joint, Inside Cover-plate — In this 
joint the plates are lapped and joined by a single row of rivets; 



STRENGTH OF BOILERS. 



270 



and a plate is worked inside and riveted through the shell 
with a single row of rivets, which are spaced twice as far apart 
as the rivets in the lap. In making up the joint all three rows 
of rivets may be driven at the same time. The lapped joint 
only is calked ; the pitch of rivets through the lap must con- 
sequently be small enough to give sound calking. The outer 
rows of rivets are not controlled by this rule. 

We will here consider a strip having the width a, Fig. 123, 
equal to twice the pitch of the rivets in the lap. Such a strip 
will be held by two rivets in the lap and by one rivet in an 
outer row. 

Assume the following dimensions: 

Thickness of shell and of cover-plate, t = 5/16. 

Diameter of rivets (iron), d — 3/4. 

Pitch of rivets in lap, p = 1 j. 

Pitch of outer rows of rivets, P— 3J. 

Shearing resistance of iron rivets per square inch or f s = 
38,000 lbs. 

The joint may fail in one of five ways : 



( * > 


JO c 


|> c 


> 


lope 


)O0QP 


© c 


)-«-( 


. P y 

) 






— 1 



Fig. 123. 
1st. Tearing between outer row of rivets. The resistance is 
(P-d)tf t - 47,270. 



280 steam-boilers, 

2d. Tearing between inner row of rivets, and shearing 
outer row of rivets. The resistance is 

(/>- 2d)tf t + *ff, = 5i, I5 o. 

4 

Since the rivets are iron, f = 38,000. 

3d. Shearing three rivets. The resistance is 

^-7-/5=50,350. 
4 

4th. Crushing in front of three rivets. The resistance is 
$tdf e = 66,800. 

5 th. Tearing at inner row of rivets and crushing in front 
of one rivet in outer row. The resistance is 

{P -2d)tf + tdf = $6,641. 

The strength of a strip of plate 3^ inches wide is 

I tf t = 60, 160. 

The least resistance is offered by the first method, giving 
for the efriciency 

47,270 
IOOX 6o7T6o := 7 8 - 6 P ercent - 

If the inside cover-plate is thinner than the shell, addi- 
tional complication will be introduced into the calculations 
for resistance. 

Double-riveted Lap-joint with Inside Cover-plate. — 
The arrangement of this joint is shown by Fig. 124. Assume 
the dimensions: 

Thickness of shell and of cover-plate, / = 7/16. 

Diameter of rivets (steel), d = 3/4. 

Pitch of rivets in lap, 2\\. 

Pitch of outer rows of rivets, P = 4. 



STRENGTH OF BOILERS. 

The methods of failure are: 

1st. Tearing at outer row of rivets. 

Resistance (P - d)tf t = 78,210. 

2d. Shearing four rivets. 

47td* 
Resistance — - f s = 79,56c. 



281 



1 J 




I 


i— < 


|> o 6 


m 


fo°J%°o°o 


M 


) c^p-^ © 


[1 1 __ 


U^ 







Fig. 124. 

3d. Tearing at inner row and shearing outer row of rivets. 
A strip having the width of the pitch of the outer row of 
rivets will be weakened at the rivets in the lap to the extent 
of one rivet-hole and half another rivet-hole. The resist- 
ance is 

Ttd 2 

(P-Hd)tf t + —f 8 = 89,080. 

4th. Crushing in front of four rivets. 

Resistance \tdf — 124,640. 

5 th. Tearing at inner row of rivets and crushing in front 
of one rivet. 

Resistance (P- \\d)tf t + tdf = 100,350. 



282 STEAM-BOILERS. 

Strength of strip 4 inches wide, 
Ptf t =9 6 >2 50. 

T-/V • 78,2IO 

Efficiency = IOO X 6 =81.3 per cent. 

Double-riveted Butt-joint. — The joint shown by Fig. 
125 has a cover-plate inside and another, narrower, outside. 
There are two rows of rivets on each side of the joint. The 
inner rows are nearer together and pass through both cover- 
plates. 




Fig. 125. 

The outer row of rivets are wider apart and pass through 
the inner cover-plate only. 

The dimensions assumed are: 

Thickness of the plate and of both cover-plates, t = 7/16. 
Diameter of rivets (iron), 15/16 inch. 
Pitch of inner row of rivets, 2f. 
Pitch of outer row of rivets, 5J. 

There are five ways in which the joint may fail : 
1st. Tearing at outer row of rivets. The resistance is 

(P-d)tf t = 103,770. 



STRENGTH OF BOILERS. 



283 



2d. Shearing two rivets in double shear and one in single 
shear. If the plate pulls out from between the cover-plates 
shearing off the rivets, then the rivets in the inner row must 
be sheared through on both sides of the plate, or they are in 
double shear. The outer row of rivets are sheared at only one 
place. There are, consequently, five sections of rivets to be 
sheared for a strip as wide as the larger pitch. The resist- 
ance is 

5nd> 

— — /,= 131,100. 
4 

3d. Tearing at inner roiv of rivets and shearing one of the 
outer row of rivets. The resistance is 

72 

{P-2d)tf t +—f,= 107,430. 

4th. Crushing in front of three rivets. The resistance is 

$tdf e — 116,880. 

5 th. Crushing in front of two rivets and shearing one 
rivet. The resistance is 

7Td* 

2tdf + — /, = 104, 140. 

4 

The strength of a strip 5J inches wide is 

Si X T \ Xft= 126,560. 
The efficiency is 

103,770 

100 — 7 — 7 r- = 82 per cent. 
126,560 r 

Triple-riveted Butt-joint. — The joint shown by Fig. 126 
has three rows of rivets on each side. Two rows pass through 
both cover-plates, and the third or outer row passes through 
the inner cover-plate only. 



284 



STEAM-BOILERS. 



The dimensions are: 

Thickness of shell, t = 7/16. 
Thickness of both cover-plates, t c = 3/8. 
Diameter of rivets (steel), d = 15/16. 
Pitch, inner rows, / = 3§. 
Pitch, outer row, P= J\. 




Fig. 126. 



The joint may fail in one of five ways : 

1st. Tearing at outer row of rivets. The resistance is 

(P-d)tf t = 151,890. 

2d. Shearing four rivets in double shear and one in single 
shear. The resistance is 



Qnd* 



f s = 279,450. • 



3d. By tearing at middle row of rivets {where the pitch is 
3-f inches) and shearing one rivet. The resistance is 

(P- 2d)tf + 7t —f i = 160,340. 



STRENGTH OF BOILERS. 285 

4th. By crushing in front of four rivets and shearing 
one rivet. The resistance is 

n d* 

4dtf c + / = 186,830. 

4 

5th. By crushing in front of five rivets. Four of these 
rivets pass through both cover-plates and will crush at the 
shell-plate. The fifth rivet passes through the inner cover- 
plate only, and will crush at that plate, since the cover-plates 
are thinner than the shell-plate. The resistance is 

A dtf + dt c f c = 189,170. 

The strength of a strip of plate 7\ inches wide is 

Ptf= 174,370. 

The efficiency is 

151,890 
100 X — = 87 per cent. 

Quadruple Riveted Butt-joints with two cover-plates. 
Fi^.127 shows such a joint. 

Thickness of shell, t = iJ2 inch. 

Thickness of both cover-plates, ^ = 7/16 inch 

Diameter of rivets (steel), J =15/16 inch. 

Pitch of inner row, p = 2> I inches. 

Pitch of second row, p = $\ inches. 

Pitch of third row, T = jh inches. 

Pitch of outer row, P = i5 inches. 
The joint may fail in one of eight ways: 
1st. Tearing at the outer row of rivets. The resistance is 

(P -d)tf t = 386,700. 

2d. Tearing at the third row and shearing one rivet in the 
outer row. The resistance is 

ltd 2 
(P — 2d)tf t -\ f s = 400,410. 



286 



STEAM-BOILERS. 



3d. Tearing at the second row of rivets and shearing three 
rivets. The resistance is 

nd 2 
(P-4^)^+3-T/ s = 4 ° 2,56a 



& & 



' > 



Fig. 



127. 



4th. Double shearing eight rivets and single shearing three. 

The resistance is 

nd* 
19— -/, = 590,200. 



5/A. Crushing in front of eight rivets and single shearing three. 

The resistance is 

izd 2 
■ &dtf c + 3— -/, = 449M40. 



STRENGTH OF BOILERS. 287 

6th. Crushing in front of eleven rivets. The resistance is 

I ld// c = 489,840. 

jth. Tearing at the third row of rivets and crushing in front 
of one rivet in the outer row. The resistance is 

(P- 2 d)tft + dtf c = 413,880. 

8th. Tearing at the second row of rivets and crushing in front 
of three rivets. The resistance is 

(P - 4d) tf + 2,dtf c = 442,960. 

The strength of the solid plate is 

Ptf t = 412,500. 

The efficiency is '- = 93.7 per cent. 

Designing Riveted Joints. — One element of the design 
of a riveted joint is to secure as high an efficiency for the 
joint as is consistent with other requirements, such as a proper 
pitch for calking. 

A consideration of the example of a single-riveted lap- 
joint will show that the efficiency can be improved by increas- 
ing the diameter of the rivet and by increasing the pitch. In 
the first place, since the joint will fail by tearing between the 
rivets, simply increasing the pitch with the same size of rivet 
will give a greater efficiency. If the pitch is increased till 
the rivet fails, the failure will be by shearing. Now the 
resistance to crushing is represented by 

dtf c , 

while the resistance to shearing is represented by 

nd % 



2 88 STEAM-BOILERS. 

that is, the resistance to crushing increases proportionally as 
the diameter, while the resistance to shearing increases as the 
square of the diameter. The shearing resistance increases the 
more rapidly, and can be made equal to the crushing resist- 
ance by using a larger rivet. Of course this will demand a 
further increase of pitch. 

In the case of the single-riveted lap-joint now under dis- 
cussion, the proper proportions for a joint that shall be equally 
strong against shearing, tearing, and crushing can be calculated 
directly. The usual way is to determine the diameter of the 
rivets by making them equally strong against shearing and 
crushing. Equating the expressions for crushing and shearing 
resistance, we have 

dtf e = — /„ or d---. 
4 J,n 

For the case in hand with steel plates 7/16 of an inch thick, 
and steel rivets, the diameter will be 

rf= 95 I ooo4XA =I . 

45,000 7t ' 

Having the diameter of the rivets, we may now calculate 
the pitch by equating the shearing and tearing resistances, 
which gives 

—/. = (*- <t)*ft> or P-J t -^+ d ' 
For the case in hand we have 



45,000 7T 1.17 , 

^ = S5.°°04 xA +, ' iy " 3 - X 



The efficiency of the joint is the ratio of the resistance to 



STRENGTH OF BOILERS. 289 

tearing between the rivets to the strength of a strip of plate 
having a width equal to the pitch, so that the efficiency is 

flp-d)t = p-d 

fspt P ' 

In the case in hand the efficiency is 
1 3.2 — 1. 17 



00 3.2 



63.4 per cent. 



But the pitch calculated in this method is too great for 
proper calking with a plate of the given thickness. 

The double-riveted lap-joint has three possible ways of 
failure, which lead to two equations for finding the diameter 
and pitch of rivets. Equating the shearing and crushing 
resistance for two rivets, we have 

2- r f, = 2dtf„ or d = J ^ ^, 
4 Js n 

which will give the same size rivet for a plate of a given 
thickness as would be found for a single-riveted joint. Now 
this method has been found to lead to too large a rivet for a 
single-riveted joint, where a strip having a width equal to the 
pitch carries one rivet. In the double-riveted joint such a 
strip carries two rivets, and consequently it is the more cer- 
tain that the method proposed will give too large a rivet, and 
of course too large a pitch for proper calking. The advan- 
tage of double riveting is that smaller rivets may be used to 
provide the requisite shearing resistance, and the plate may 
be less cut away at the section between rivets. 

In designing a double-riveted lap-joint it is customary to 
assume a diameter for the rivets and then determine the pitch 
by equating the shearing resistance of two rivets to the tear- 
ing resistance between the rivets. If the resulting pitch is too 
large for proper calking, the diameter of the rivets must be 



290 STEAM-BOILERS. 

reduced. If, on the contrary, the resulting pitch is less than 
may be allowed, a slightly larger diameter and pitch may be 
used. 

A design of a joint like the single-riveted lap-joint with 
inside cover-plate, which has a wide and a narrow pitch, 
involves some difficulty and complexity. The fundamental 
idea of such a joint is to make the resistance to tearing at the 
inner row of rivets (when the pitch is small) plus the shearing 
of the outer row of rivets greater than the resistance to tear- 
ing at the outer row of rivets (when the pitch is larger). To 
insure this condition we may proceed as follows: Equate the 
resistance to tearing at the outer row of rivets to the resist- 
ance to tearing at the inner row plus the resistance to shearing 
one rivet at the outer row. This gives 



(P - d)tf t = (P - 2d)tf t + ^/„ 

4 
whence 

d=% 



The result is the minimum diameter of rivets allowable. 
We may now choose a slightly larger diameter of rivets, and 
then determine the pitch in three different ways, namely, by 
equating the resistance to tearing at the outer row of rivets, 
in succession, to the resistance to shearing of three rivets, 
to the resistance to crushing in front of three rivets, and 
to the resistance to tearing between the inner rows of rivets 
and compression before one rivet. The smallest pitch 
obtained will be the correct one to use with the given diam- 
eter of rivet. Should the efficiency of the joint be unsatis- 
factory, an attempt may be made to raise the efficiency by 
increasing the diameter of the rivets. 



STRENGTH OF BOILERS. 201 

In the preceding pages it has been assumed that the strength 
of a rivet in double shear is twice that of a rivet in single shear. 
Many designers use a lower value per square inch in double 
shear than in single shear. There is but little evidence to show 
that there is any justification for this. 

The effects of crushing and shearing are so combined that it 
is difficult to get any data on double shear that is reliable. A 
careful study of all the tests made at the Watertown Arsenal, 
and of those made at the Massachusetts Institute of Tech- 
nology, failed to give any evidence that would warrant using 
a lower value per square inch for double shear than for single 
shear. 

Practical Considerations. — In proportioning a riveted 
joint, the following considerations, some of which have already 
been mentioned, must receive attention: 

The pitch of rivets near a calked edge must not be too great 
for proper calking. 

Rivets must not be too near together for convenience in 
driving. 

Punched holes must have a diameter greater than the 
thickness of the plate. 

A riveted seam must contain a whole number of rivets. 
Again, it is desirable that similar seams, as for example the 
longitudinal seams for the several rings of a cylindrical boiler, 
shall have the same pitch. 

It is evident that the design of a boiler-joint cannot be 
considered apart from the general design of the boiler. 

Flues. — The tendency of internal pressure in a thin hol- 
low cylinder is to give it a true cylindrical shape; conse- 
quently, with fair workmanship, the formulae for thin hollow 
cylinders may be applied to the calculation of boiler-shells 
subjected to internal pressure. But the tendency of external 
pressure is to exaggerate any imperfection of shape, and 
cylindrical flues fail by collapsing. 



292 STEAM-BOILERS. 

The pressure at which a flue will collapse can be found by 
direct experiment only. 

The earliest and for a long time the only tests on the 
collapsing of flues were those made by Fairbairn, and pub- 
lished in the Transactions of the Royal Society, in 1858. All 
of the tubes tested were 0.043 of an inch thick; they varied 
in diameter from 4 inches to 12 inches, and in length from 20 
inches to 60 inches. From these tests he deduced the em- 
pirical formula 



806,300 X t 219 



in which / is the length of the tube in feet and <a?and / are 
the diameter and thickness in inches, while/ is the collapsing 
pressure in pounds. per square inch. Sometimes the exponent 
of / is made 2 instead of 2.19, for sake of simplicity. As /is 
commonly a proper fraction, the use of a smaller exponent 
will give a higher calculated collapsing pressure. 

The tubes in this series were too small, and more especially 
too thin, to serve as a proper basis for the calculation of boiler- 
flues. It is quoted because it has been widely used, and is 
now used by some engineers. It sometimes gives a calculated 
pressure higher and sometimes lower than that at which flues 
will collapse, and its use is liable to lead to disappointment if 
not to disaster. 

The following table gives the results of some tests on 
larger boiler-flues, taken from Hutton's " Steam-boiler Con- 
struction." The table gives the dimensions and the actual 
collapsing pressure, and also the collapsing pressure by Fair- 
bairn's rule and by a rule proposed by Hutton. 



STRENGTH OF BOILERS. 



293 



EXPERIMENTS ON THE COLLAPSING PRESSURE OF BOILER. 

FLUES. 



Where or by Whom Made. 



By Fairbairn 

By Fairbairn 

By Fairbairn 

By Fairbairn ... 

Engineering Dept., U. S. N. 

At Greenock 

By Knight. . 

By Knight 

By Kntght 

By J. Howden & Co., Glas- 
gow 



Dimensions. 



Q-S 
— c 
t«—> 

5° 



7.87 



33- 
42 
42 

54 
33 
36 
36 
36 

43 



3 



276 

360 

420 

300 

36 

86 

24 

24 

48 

23 



e a 



•C2 



Collapsing Pressure in 
Pounds per Square Inch. 



Ss« 

■°a 

c <u 
3 a 
o x 



no 

99 
97 
127 
128 
45o 
235 
468 
390 

840 



sx 


5s-= 

.O 3 


•0 * 


-atf 


rt.is 


«« 


^ 


32 








of 3 


Ufc, 


uK 


6 


7 



109 

81 

78 

108 

311 
740 

700 

1568 

784 

2758 



114 
113 

IOO 

119 

120 

436 
218 
490 
350 

842 



On the whole the rule proposed by Hutton gives the most 
concordant results; in most cases Hutton's rule gives a cal- 
culated collapsing pressure that is smaller than the actual 
collapsing pressure; in no case is the calculated result very 
largely in excess. Fairbairn' s rule in some cases shows a very 
close agreement with experiment, but in others it shows a 
dangerous excess. 

Hutton's rule is 

Ct* 
p= dVi' 



in which I is the length in inches, d is the diameter in 



294 STEAM-BOILERS. 

inches, and / is the thickness in thirty-seconds of an inch. 
C is a constant which Hutton makes 600 for iron and 660 for 
steel. 

Mr. Michael Longridge, as a result of an investigation of 
many boiler flues, most of which have endured service for 
years, but some of which failed, gives a rule in the same form 
but with a constant 540 instead of 600. 

For oval tubes and flues it is recommended that the above 
rules be applied, using for the diameter twice the maximum 
radius of curvature. 

Strengthened Flues. — It is clear from inspection of the 
preceding table of tests on boiler-flues that the collapsing 
pressure decreases as the length of the flue increases. Account 
is taken of this in Hutton's formula, by introducing the 
square root of the length into the denominator of the expres- 
sion for calculating the collapsing pressure of a flue. Stating 
the proposition in the converse manner, the reason why a 
short flue is the stronger is that the ends of the flue are 
kept in a circular form by the plates to which the flue is 
riveted. 

It has been customary to strengthen plain flues by the aid 
of rings placed at regular intervals. The section of a ring 
made of angle-iron is shown by Fig. 128a. The ring is riveted 
to the flue at intervals, a thimble being placed over each rivet 
to give space for circulation of water between the ring and 
the flue. The rings were sometimes solid, made of one piece 
of angle-iron bent up and welded. Most frequently the ring 
was in halves, which were merely belted together at the joint. 
Such rings could be easily removed when the flue was taken 
out of the boiler. 

A better method of strengthening a flue is to make it of 
short pieces so joined at the ends as to make stiffening rings. 
Fig. 128 shows three ways in which this can be done. At b 
is shown the Adamson ring, formed by flanging the edges of 



STRENGTH OF BOILERS. 



295 



the short lengths of flue outwardly, and riveting through a 
welded iron ring. At c is shown a welded ring of T iron, to 
which the short lengths can be riveted without flanging. This 





Fig. 128. 



method provides for calking both inside and outside. It 
does not require the flue to be flanged; but flanging by 
machinery is rapid, and does not give trouble when good iron 
or steel is used. Material that will not stand flanging should 
not be used for flues. At d is shown the bowling hoop-ring, 
which has the advantage that it provides for longitudinal 
expansion of the flue. 

Flues for Scotch and other marine boilers with furnace- 
flues, are stiffened by transverse or helical corrugations, which 
provide at the same time for longitudinal expansion. A 
number of methods of corrugating furnace-flues will be 
illustrated in connection with tests given on the following 
pages. 

Tests on Furnace-flues. — The strength of corrugated and 
other stiffened flues can be determined only by tests on full- 
sized specimens. The following tests are taken from a paper 
by Mr. B. D. Morison, read before the Northeast Coast In- 
stitution of Engineers and Shipbuilders. 



296 



S TEA M-B OILERS. 



Furnaces made with Adamson Joints. 

Tests made at the Works of Hall, Russell & Co., Aberdeen, in 
1882, and of J. Howden & Co. in Glasgow, in 1887. 



Date 

of 
Test. 


Length 
Furnace. 


0) 

c 



u 

£1 

a 

3 


> o 

C/l 

en 
V 

c 

M 



<uPm 


U l> 

r° 

en 

C- 1 c 

V- 't5 

5-SE 


c >. 

— c 

« 0*: 
SQPu 


V 
i_ 

Oh 

be 

B 
'00 

O «5 


8 + 

boX 

■Sex. 
f . 

« g 
« 


ollapsing Coeffi- 
cient reduced to 
Steel of 27 Tons 
Tensile. 






£ 


§ 


w 


O 


u 


u 


U 








1st ring 














6 ft. 5! in. total 




i" 

¥ » 














length. 




2d ring 












1882 


Length of 

rings : 

i8i". 10", 19", 

and 20" 

7 ft. \ in. total 


4 


11" 

3d ring 

15" 
3S ' 

4th ring 

1" 


43 


9/64 


3d ring 
at 700 

1st ring 
at 840, 
2d ring 


64,213 


61,918 


1887 


length. 

Length of each 

ring, 23" 


4 




43-09 




at 760, 
3d ring 
at 840, 
4th ring 
at 835 


64,240 


61,945 



Note. — No record of tensile strength of steel ; 28 tons per square inch 
assumed. The collapsing coefficients are calculated on external diameter of 
furnace over plane part. 



STRENGTH OF BOILERS. 



297 





00 




TJ 




G 




rt 




O" 




CN 




OO 




M 


<u 


„ 


u 


m 


rt 


00 


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00 


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>— 1 


3 




fc 


— 


TJ 


<n 


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+-> 


<v 


rt 


<D 


bOJ 


D 









U o 

4-» 

O TD 

* e 



3 
u 

O 















C 


1 






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3 








3 c 








1 & 






CO oj p nl 


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S| 


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3 i/ 


c 1 8 


c rt 


O O 




a c 


J 3 
u - 



c w 






O Og 


Ofa 


fa 














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■suoj, iz 





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C) 


»n 


O 


JO I331S 05 


10 CO 


vC 


cr 


co 


in 


paonpaj 


00 


t °_ 


in 


c 


n- 


vO 


juapiy303 

SuisdE|[03 


co m r^ 
r^ r^ vo 




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qiSiiaJigajis 


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CN 


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CO 


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vO 


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in 


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Oh 




CO CO 


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S-l 


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CO 


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vn 


CN 


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C 


§ 




























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O in 


o> 


M 


r-s 


CN 


2 




co -t- 




r^ 


r^ 


"* 


H 




co co 


Tt 


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in 




jo qiSu3q 




in vo 





J* 


H 
vO 




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C 


rj i_ M 


N 


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v 




















iota ; 




Its 




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r-H l-lOB 


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C 


r» co co 


r^ 


00 


CN 


O 




\C 


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O 


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vb 






1— 


M 


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„ 






— 


O 


O^ 


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a^ 




c 


1 O -co 


OO 


00 


CO 


00 




c 


JN O O -H 










V 

a 


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. "* w w 


M 


_T 


m 


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M 


1-1 


M 


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c 


1 0* - " -o 


^' 


xa 


J3 


J3 




> 4> t) 


u 


CJ 


aj 


U 






5? 


; 55 fa fa 


fa 


fa 


fa 


fa 



H 


tj 


1 


<u 








rt 


w 


<u 


H 


c 


O 

55 


C 




a; 




w 




a> 




H 



298 



S TEA M-B OILERS. 




1! 

'35 o 

Oh 


•0 
1- 



V 

u 



Collapsing- 
Coefficient 
reduced to 
Steel of 
27 Tons Ten- 
sile. 


OO O O OO O 
O ^ O <* N 

in in <y> « 
vO 00" O*co" in 
in m in «j- in 


Ultimate 
Tensile 
Strength 
of Steel 
Assumed. 


00 CO CO 00 CO 
W M N N W 


oX 


m r-~co co 

OOO i-o 

OO O t^M 

OO* 0* (> 0" N 
invO in in in 


ex . 

as 

On" 


in O O O in 
en in r^ r- m 
co 00 O in in 


Mean Diam- 
eter 
in Inches. 


m (N 00 -i-O 

M *-i O en CJ 

O^ C>CO CT> O 


c c 

rt U5 1- " 

v u> a 


Oco W O «3" 
m **f tJ- tJ- in 
in in rf ^ en 


d! 

3- 


J J »• j 'lo 

«shf»tai»H'«*»> ,0 H 
invO O O vO 

O O O O vO 


(A 

H 

Q 


May, 1888 

Do 

Do * 

Do 



S2 eg 

H 3 

c 



STRENGTH OF BOILERS. 



299 



00 



3 

X 



O T3 

K 3 



.2 

o 



C/3 

y ° v 
g <-> 

S « _ 

-a J Y 

f 3 p. V 






V 



had 
a 



75 



a 



8.S ~£ ~2 

O E Dh 



•suox ^ jo 
[331g ojpsonp 

-3J JU3IDIJJ3 

-03 SuisdB[[o3 



00 (> 



•1331S jo 

qiSuajig 3[;s 

-U3JJ 31BUlUIfl 



■ x •*■ a x J 

}U3IDIJJ3 

03 SuisdBi[o3 



•3JnSS3J,J 

J§uisdEi[o3 



XlIE JB J3}301B 
-IQ UI3DU3J3J 
-}}(J JS31E3JQ 



UIBJJ JO 3piS 

-VnQ J3;3oieiq 



H^ 



•spug }B ]Bl J 
jo ipSusT 

;S3}H3if) 



•suonB3njJ03 
jo jaqmn^ 



3DBU 

■jit j jo qiSusq 



<3 H 



PJOD3J O^J 



"* Tf TT 



3°° 



S TEA M-B OILERS. 




'55 °=5 
o o 



"31ISU3J, SUOl Lz 

jopajs oj paonpai 
'B 3 °D SuisdEno3 



VI (A 

jd ja "O 
*E *C g 

t! t> 2 ~ 

SXUh 



NONCOCO>-iNi-i 

co inco m co co c* O 
OO r^ m hoo <trs 



'1335S jo qjSuajJS 



MO O* O^ i* O^-^ CO 



X •+■ a * J map 



O -"to a- w cn o 

COCO h-i X^ O O O 



ajnssajj SuisdEfjo^ 



O O O m O C m 
TO in co O O r^ 
t^. r^o O co oo co i 



UI 3DU3J3JJIQ JS31B3a£) 



J3AO J353niB;Q 



UB3J^ 



m cn m co r^cc 

►- oo m o coo too 
vO O O moo oo vO r^- 



co O I m G^ C 1 |_| co 
O T I >- O m -i •-" 
ir> in co in inO O 



•pug jpng 



co ci O co co O r^ 
•3-co*- h- CO m O^O 
m in co co T m inO 



"3IPPIW 



m -t-O N inO^woo 
co inco O coco coco 
invnM coininOO 



pug lUOJg 



s t** m CT> coo 
a co -t in in in 



pug Wld 
jo q^Suag isajBajf) 



•suoijbS 
tujo3 jo aaqtun^ 



•roBiung jo qiSuaq 



m|we9|e 
cocor^r^r^r^r^ r% 



i"» r^co oo co co co oo 



Ooooooo o 



t»xj° »^a 



co co 
co oo 
** M r» r- r^ r^ r^ r-. 

- - oo oo co oo co oo 

N « CO OO ■» OO OO CO 






STRENGTH OF BOILERS. 



301 



Purves's Patent Furnaces. 



Official Tests made at Sir John Brown & Co. 's Works at 
Sheffield in 1889. 






T\»ce of Test. 



889. 



it) rt 



Dec. 23, 1890. 



9i 
9i 

9! 

9* 



a *i 
u o 



.307 

.362 
.461 

.466 

.585 
.578 

.522 



> -C 

o u 



u C 
U •- 

Q 



is 
s 5 * 

u w rt 
O 



38.78...., 

38.70 

38.70 

38.72 

38.63 

38.65.... 
38.75I.-.-- 





. 








K," 


cu 




bt> 


c 


.S^q 


2- u * 


&s x 




o'-c 


= 3 

O «5 


u 


U 



675 

700 
870 
950 

1,065 

»>*45 

1,020 



85,265 
74,834 
73.034 
78,935 
70,326 

-A -^ . 

75,718 



« tx 



28.8 
28.O 

27-3 
29-3 

23.7 



iv. r.- 



3 



o '55 

5 c 

w.£_ 4) 
C VL| 

— *j u " 

71 " « ,. 

U 

79,935 
72,161 
72,231 

72..?3& 
C6,i6o 
75,446 



Corrugations spaced 9" apart. Not very full records kept. 

Note.— The collapsing coefficients are calculated on diameters of furnaces 
over flats. 



3 02 



STEAM-BOILERS. 



U 
ct 

C 
u 

3 



00 



J 



c 



<L) 

C cr 

C/) <U 

3 J 

tn -g 

s ^ 

■S ° 

S E 



:0 

O 

H 



O 



« ~ ^ 8 c § 

p t;&!J:l 



uaj^ suoj ^z jo 
paiSoi psonp 

3JJ303sdH||03 



»n CO CM 

vO vO CO 



•paiS jo 
qiSuajis 3[is 
-U3X ajBiupin 



vpo3 sdBiioo 



m vo O 



s-inssajj 
SuisdBno3 



O O 



}JB<jAuB }B J313 
-U1BIQ Ul 3DU3 
■J 3 JJ?a JS31B3Jf) 



Tt" CM 

IN vd CO 

CO ^ \ 

IN HI M 



in 



•saqoui ui 

J3J3UIBIQ UB3J^ 



uT3 



O co 

■<* o 
en en 



CM co 






O HI \T> IN 

tt ^r ** ""> 
tn tn rf "ri- 



spug ib jbu jo 

Ul3U311S3?B3JO 



-suo.UBSru.103 
jo aaquinM 



•3DBU 

-jnji jo inSuaq 



en 


en 


en 


en 


en 


en 


in 


en 


O 


M 


O 


r^ 


CM 


r-N 


r^ 


in 


en 


vO 


CO 


en 


-r 


■* 


m 


in 



Qn O** O^ s O^ C7* 



vO O O 






o o 
Q P 



STRENGTH OF BOILERS. 303 

Discussion of Results of Tests on Flues. — The stress 
in a thin hollow cylinder subjected to external fluid pressure 
may be calculated by an equation having the same form as 
that for a cylinder subjected to internal pressure; the equa- 
tion may be deduced by a similar method. Thus the stress 
will be 

s r 

in which / is the pressure per square inch, r is the radius and 
/ is the thickness, both in inches. In the table we have a 
column giving the coefficient of collapse calculated by the 
expression 

PD 
T' 

in which Pis the pressure, D is the diameter, and 7* is the 
thickness. The coefficient appears consequently to be twice the 
compressive stress in the flue at the time of collapsing. This 
coefficient is fairly regular for each style of furnace, and is 
somewhere near the tensile strength of the metal from which 
the flue is made; in some cases it is less and in some more 
than the tensile strength. Now soft steel in the form of short 
cylinders will begin to flow when the compressive stress in a 
testing-machine is about equal to the strength of pieces used 
for tensile tests. In other words, the tensile and compressive 
strengths are about equal. The furnaces tested appear, 
then, to have collapsed when the compressive stress was half 
the ultimate compressive strength of the metal. Now the 
limit of elasticity for both tension and compression, for soft 
steel, is about half the ultimate strength, so that the collapse 
occurred somewhere about the elastic limit. We should not, 
however, attribute too much importance to this considera- 
tion, but it will be better to follow ordinary practice and 
consider the equations used for calculating* the safe working 



3°4 



STEAM-BOILERS. 



pressure on flues to be empirical, and to depend directly on 
experiment. 

Rules for Working Pressure on Flues. — There are three sets 
of rules for working pressure on flues, which need be considered, 
namely, those of the British Board of Trade, those of Lloyd's 
Marine Insurance Underwriters, and those of the United States 
Inspectors of Steam-vessels. These rules are changed from time 
to time, and include certain directions to inspectors that need 
not be given here; if a boiler is built for inspection under these 
or any other rules the only safe way is to obtain the current 
edition of the rules and see that the boiler conforms thereto, 
and also that the boiler is properly proportioned according to 
the best information that can be obtained by the designer. 

Rules for Plain Flues. — The rules for flues as given by the 
United States Board of Supervising Inspectors — Steamboat In- 
spection Service — as amended January, 191 1, are: 

Plain, Lap- welded Steel Flues, 7 to 18 Inches Diameter. 

Working pressures and corresponding minimum thicknesses 
of wall for long, plain, lap-welded, and seamless steel flues, 7 
to 18 inches diameter, subjected to external pressure only, shall 
be determined by the following table and formula: 





Working Pressure in Pounds per Square Inch. 


Outside 
















Diameter 


[00 


[20 


140 ] 


60 


180 


200 


220 


of Flue. 
















Inches. 




Thickness of Flue in Inch 


es. Safety Factor, 5. 






7 


152 


160 


.168 


177 


.185 


193 


201 


8 


174 


183 




193 


202 




211 


220 


229 


9 


196 


206 




217 


227 




237 


248 


258 


10 


218 


229 




241 


252 




264 


275 


287 


11 


239 


252 




265 


277 




290 


303 


316 


12 


261 


275 




289 


303 




317 


330 


344 


13 


283 


298 




313 


328 




343 


358 


373 


14 


301 


320 




337 


353 




369 


385 


402 


15 


323 


343 




361 


378 




396 


413 


430 


16 


344 


366 




385 


404 




422 


440 


459 


17 


366 . 


389 




409 


429 




448 


468 


488 


18 


387 ' 


412 




433 


454 




475 


496 


5i6 



STRENGTH OF BOILERS. 305 

Thicknesses in this table were calculated by formula 

_ [(F X P) + 1386] D 
86,670 

where D = outside diameter of flue in inches. 

T = thickness of wall in inches. 
P = working pressure in pounds per square inch. 
F = factor of safety. 

This formula is applicable to lengths greater than six diame- 
ters of flue, to working pressures greater than 100 pounds, to 
outside diameters of from 7 to 18 inches, and to temperatures 
less than 650 F. 

When flues are constructed of plates made in sections and 
efficiently riveted together, not less than 24 inches in length, 
minimum thickness 0.25 of an inch, over 6 and not exceeding 
18 inches in diameter, the working pressure shall be calculated 
by the following formula: 

p _ 8100 T 
D 

where P = the working pressure in pounds per square inch. 
T = the thickness in inches. 
D = outside diameter in inches. 
The working pressure allowable on seamless, riveted, or on lap- 
welded flues over 18 inches in diameter up to and including 28 
inches in diameter, made in sections not less than 24 inches in 
length, efficiently riveted together, sections not to exceed three 
and one half times the diameter of the flue, when subjected to 
external pressure only, shall be determined by the following 
formula: c c 

P= ^[(18.75 XT) -(LX1.03)] 

where P = the working pressure in pounds per square inch. 
D = the outside diameter of the flue in inches. 
L = the length of flue in inches not to exceed 3^ diameters. 
T — thickness of wall in sixteenths of an inch. 



306 STEAM-BOILERS. 

Furnace Strength. — The United States Board of Supervising 
Inspectors give the following rules, amended January, 191 1, for 
figuring the strength of different furnaces. 

The tensile strength of steel used in the construction of cor- 
rugated or ribbed furnaces shall not exceed 67,000 and be not 
less than 54,000 pounds; and in all other furnaces the minimum 
tensile strength shall not be less than 58,000 and the maximum 
not more than 67,000 pounds. The minimum elongation in 
8 inches shall be 20 per cent. 

All corrugated furnaces having plain parts at the ends not 
exceeding 9 inches in length (except flues especially provided 
for), when new, and made to practically true circles, shall be 
allowed a steam pressure in accordance with the following 
formula : 

D 

Leeds Suspension Bulb Furnace. 
F _ CXT 
D 
where P = pressure in pounds. 

T = thickness in inches, not less than five sixteenths of 

an inch. 
D = mean diameter in inches. 

C = a constant, 17,300, determined from an actual de- 
structive test under the supervision of the Board, 
when corrugations are not more than 8 inches 
from centre to centre, and not less than 2\ inches 
deep. 

Morison Corrugated Type. 

CX_I 
D 

where P = pressure in pounds. 

T = thickness in inches, not less than five sixteenths of 
an inch. 



STRENGTH OF BOILERS. 307 

D = mean diameter in inches. 

C = 15,600, a constant, determined from an actual de- 
structive test under the supervision of the Board 
of Supervising Inspectors, when corrugations are 
not more than 8 inches from centre to centre 
and the radius of the outer corrugations is not 
more than one half of the suspension curve. 
[In calculating the mean diameter of the Morison furnace, 
the least inside diameter plus 2 inches may be taken as the mean 
diameter, thus — 

Mean diameter = least inside diameter + 2 inches.] 

Fox Type. 
P _CXT 
D 

where P = pressure in pounds. 

T = thickness in inches, not less than five sixteenths. 

D = mean diameter in inches. 

C = 14,000, a constant, when corrugations are not more 

than 8 inches from centre to centre and not less 

than 1 J inches deep. 

Purves Type. 
P _CXT 
D 
where P = pressure in pounds. 

T = thickness in inches, not less than seven sixteenths. 
D = least outside diameter in inches. 
C = 14,000, a constant, when rib projections are not 
more than 9 inches from centre to centre and not 
less than if inches deep. 

Brown Type. 
r _ CXT 
D 

where P = pressure in pounds. 

T = thickness in inches, not less than five sixteenths. 



308 STEAM-BOILERS. 

D = least outside diameter in inches. 

C = 14,000, a constant (ascertained by an actual de- 
structive test under the supervision of this Board), 
when corrugations are not more than 9 inches 
from centre to centre and not less than if inches 
deep. 

The thickness of corrugated and ribbed furnaces shall be 
ascertained by actual measurement. The manufacturer shall 
have said furnace drilled for a one-fourth-inch pipe tap and 
fitted with a screw plug that can be removed by the inspector 
when taking this measurement. For the Brown and Purves 
furnaces the holes shall be in the centre of the second flat; for 
the Morison, Fox, and other similar types in the centre of the 
top corrugation, at least as far in as the fourth corrugation from 
the end of the furnace. 

Type Having Sections 18 Inches Long. 

CX_T 
D 

where P = pressure in pounds. 

T = thickness in inches, not less than seven sixteenths. 

D = mean diameter in inches. 

C = 10,000, a constant, when corrugated by sections not 
more than 18 inches from centre to centre and 
less than 2\ inches deep, measuring from the 
least inside to the greatest outside diameter of 
the corrugations, and having the ends fitted one 
into the other and substantially riveted together, 
provided that the plain parts at the ends do not 
exceed 12 inches in length. 

Adamson Type. 

When plain horizontal flues are made in sections not less 
than 18 inches in length, and not less than five sixteenths of an 
inch thick, and flanged to a depth of not less than three times 



STRENGTH OF BOILERS. 309 

the diameter of rivet hole plus the radius at furnace wall (inside 
diameter of furnace), the thickness of the flanges to be as near 
the thickness of the body of the plate as practicable. 

The radii of the flanges on the fire side shall be not less than 
three times the thickness of plate. 

The distance from the edge of the rivet hole to the edge of 
the flange shall be not less than the diameter of the rivet hole, 
and the diameter of the rivets before driven shall be at least 
one fourth inch larger than the thickness of the plate. 

The depth of the ring between the flanges shall be not less 
than three times the diameter of the rivet holes, and the ring 
shall be substantially riveted to the flanges. The fire edge of 
the ring shall terminate at or about the point of tangency to 
the curve of the flange, and the thickness of the ring shall be 
not less than one half inch. 

The pressure allowed shall be determined by the following 
formula : 

Adamson Furnaces in Sections of not less than 18 Inches 

in Length. 

P= ^'[(18.75 XT) -(1.03 XL)] 

where P = working pressure in pounds per square inch. 
D = outside diameter of furnace in inches. 
L = length of furnace in inches. 
T = thickness of plate in sixteenths of an inch. 

Cylindrical riveted flues and furnaces made in sections of 
not less than 18 inches in length fitted one into the other and 
substantially riveted, combustion chambers for vertical sub- 
merged tubular boilers in the shape of a frustum of a cone, con- 
structed to a practically true circle, shall be allowed a steam 
pressure according to the following formula: 

P = SijS [(18.75 XT) -(1.03 XL)] 



3 1 STEA M -BOILERS. 

where P = working pressure in pounds per square inch. 

D = outside diameter of furnaces in inches, or outside 

mean diameter of cone top in inches. 
L = length of furnace or flue in inches. 
T = thickness of furnace or cone top in sixteenths of an 

inch, not to be less than five sixteenths of an 

inch. 

When diameter of plain furnaces and flues used in vertical 
type of boilers or mean diameter of cone tops exceeds 42 inches, 
they shall be deemed a flat surface and must be stayed in ac- 
cordance with rules governing flat surfaces. If a greater work- 
ing pressure than given by formula is desired for mean diameters 
under 42 inches, the flues or cone tops shall be substantially 
stayed for such additional pressure. 

Fire-tubes. — The thickness usually given to fire-tubes to in- 
sure sound welding and to provide for expanding into the tube- 
sheets is in excess of that required to prevent collapsing. There 
appears, however, to be no experiments to show the actual 
collapsing pressure for such tubes. 

The joint made by expanding the tubes into the tube-sheets 
of locomotive and cylindrical tubular boilers has been found 
both by experiment and practice to be strong enough to secure 
the tube-sheet without additional staying. 

Girders. — When a flat surface cannot conveniently be stayed 
directly, it is customary to stay the surface to girders properly 
supported at the ends or elsewhere. The crown-bars of the 
locomotive boiler shown on Plate II, and the girders over the 
combustion-chamber of the marine boiler shown by Fig. 11, 
page 17, may be taken as examples. Again, the channel irons 
which are riveted to the flat heads of the cylindrical boiler 
shown by Plate I act as girders. 

The load which a girder of given material can safely carry 
depends on the form and dimensions of the girder, and on the 
manner of supporting and loading the girder. Some girders, 
like those over the combustion-chamber in Fig. 11, may be 



STRENGTH OF BOILERS. 3II 

calculated by the simple theory of beams; others, like crown- 
bars for locomotives and the channel-bars on Plate I, can be 
properly calculated only by the theory of continuous girders. 

A proper understanding of the theories of beams and of 
continuous girders can be obtained from standard works on 
applied mechanics. An adequate statement of even the 
theory of beams is out of place in a work on boilers; an 
incomplete statement is unadvisable, since it is liable to be 
misleading. One simple example will be worked out as an 
illustration of the use of the beam theory in boiler-design. 

As an example, we will take the girders over the combus- 
tion-chamber of the marine boiler shown by Fig. 11, page 17. 
The girders are spaced 7 inches apart, and each carries three 
stays spaced 6J inches apart. The load on each stay-bolt at 
160 pounds steam-pressure is 

j X 6 J X 160 = 7000 pounds, 

and the total load on one girder is 21,000 pounds- The sup- 
porting force at each end of the girder is 10,500 pounds. The 
span of the girder is 22 J- inches, and the half-span is \\\ 
inches. The bending-moment at the middle of the girder 
due to the supporting force acting upward, and to the load 
on one bolt acting downward, is 

10,500 x u| — 7000 X 6£ = 74,375 = M. 

Each girder is made of two plates each 5/8 of an inch thick, 
and 7 inches deep. The moment of inertia of the section of 
the girder at the middle is 

T V X 2 X f X 7 3 = /- 
The distance of the most strained fibre is 
7~2 = 3£=^. 



312 STEAM-BOILERS. 

The working fibre-stress is consequently 

f _My_ 74 375 X 3J _ g 
/ - / -_ VX 2XfX7 3 ~ 7 7 

pounds per square inch. 

Stayed Flat Plates. — The method of calculating the 
stresses in a flat plate supported at regular intervals by stays 
or stay-bolts, such as the sides of a locomotive fire-box, is 
treated in the theory of elasticity, under the heading of 
" indefinite plates which are firmly held at a system of points 
dividing them into rectangular panels." A complete solution 
of this problem is possible only when the panels are squares, 
that is, when the rows of stays are equidistant longitudinally 
and transversely. 

If the steam-pressure is represented by/, the thickness of 
the plate by /, and the pitch of the stays by a y then the 
direct working stress, which is a tension at certain places and 
a compression at others, is given by the formula 

S= 9?* 

The maximum deflection is given by the equation 

I pcf 

in which E is the modulus of elasticity of the material. 

If the sheets of a locomotive fire-box, or other stayed 
plates, have a direct tension or compression, proper allowance 
must be made for it. 

If stays or stay-bolts are in rows that are not equidistant 
each way, as for example the through-stays in the steam- 
space in Fig. ii, page 17, then the largest pitch maybe used 
in the above equations. The actual stress will in such case be 
less than the calculated stress by an unknown amount. If, 



STRENGTH OF BOILERS. 313 

further, stays are arranged irregularly, the greatest distance 
in any direction may be used in the equations, but the calcu- 
lated stress may then be very different from the actual stress; 
it is, however, always the larger. 

As an example, we may calculate the stress in a side sheet 
of the locomotive fire-box shown on Plate II. Here the 
rows of rivets are four inches apart each way, the plate is 
5/16 of an inch thick, and the steam-pressure is 170 pounds. 
The maximum stress is 

/= l(Af I7 ° = 6l9 °- 

Now the crown-bars are bedded on and are partly sup- 
ported by the side sheets of the fire-box. The crown-sheet 
is 72 inches long and 45! inches wide, and has an area of 

72 X 45ft = 3285 
square inches, and is subjected to a pressure of 

3285 X 170 ■= 558,450 

pounds. The distribution of this load between the side 
sheets and the sling-stays can be determined only by the cal- 
culation of the crown-bars as continuous girders, and may be 
disturbed by the expansion of the fire-box and by other 
causes. If it be assumed that the side sheets carry half the 
load on the crown-bars, then one side sheet will carry one 
fourth of 558,050, or 139,512 pounds. The side sheet is 72 
inches long and 5/16 of an inch thick, so that the stress per 
square inch from the load on the crown-bars is 

139,512 -r- 72 X A = 62QO 

pounds, — about as much as the stress calculated above. The 



314 S TEA M-BOIL ERS. 

total compression on the side sheet is therefore about 12,400 
pounds per square inch. 

This calculation, which appears sufficiently simple, illus- 
trates the danger of making calculations by formulae without 
knowing how they are derived and how they should be 
applied. The formula for staying given above is often 
quoted without any reference to tensile or compressive stress 
on the stayed sheet, from other causes; the use of such a 
formula by one who is unfamiliar with the theory of elasticity 
may lead to serious error in design. 

Factor of Safety.— The reciprocal of the ratio of the 
working pressure of a boiler to the pressure at which the 
boiler or any part of a boiler may be expected to fail quickly, 
is called the factor of safety for the boiler or for that part of 
the boiler. 

It is commonly recommended by writers that a factor of 
safety of six shall be used for boilers; probably such a factor 
would be economical for a boiler that is expected to work 
continuously for many years, as it allows a margin for deteri- 
oration. If the stresses coming on the parts of a boiler can 
be determined, a general factor of five will give sufficient 
security. If the boiler is carefully watched, a factor of four 
may be used; many boilers are worked with this factor. The 
use of an excessively large factor of safety, for example of the 
factor nine for flues calculated by Fairbairn's equation, shows 
a lack of confidence in the method. It is proper to make 
allowance for corrosion of parts like stays: this may be done 
either by using a larger factor of safety, or by a direct allow- 
ance; thus all stays, whatever their diameters, may have an 
eighth of an inch added to the diameter to allow for corrosion. 
It is of course proper in any structure to make small but im- 
portant members, such as stays in boilers, large enough to 
place them beyond any suspicion of failure. 

Hydraulic Tests of Boilers. — It is customary to subject 
new boilers to a water-pressure considerably in excess of the 
working pressure, to discover any leaks at riveted joints, at 



STRENGTH OF BOILERS. 315 

the tube-sheets, or elsewhere; should there be any gross 
defect of design or workmanship it will be developed by this 
hydraulic test. Old boilers after repairs are subjected to a 
hydraulic test for the same purpose, but the pressure is not 
carried so high as for new boilers. 

The pressure applied during a hydraulic test is seldom 
more than once and a half the working pressure, and as most 
boilers have an actual factor of safety of not more than five, 
and frequently of four, it is apparent that the recommenda- 
tion of some authors, that the test pressure should be twice 
the working pressure, cannot ordinarily be followed without 
danger of injuring the boiler. With a factor of safety of six 
there should be no danger of injuring the boiler by applying 
a hydraulic pressure equal to twice the working pressure. 

It should be borne in mind that some of the worst stresses 
that come on the different parts of the boilers are due to 
unequal expansion and contraction, and that such stresses are 
not set up during a hydraulic test. Finally, the fact that a 
boiler has successfully withstood a hydraulic test is not a con- 
clusive proof that it is safe; too many unfortunate explosions 
of boilers, more frequently old boilers, after a hydraulic test, 
have shown this. 

The safety of a boiler is to be insured by careful and cor- 
rect design, honest and thorough workmanship, and intelli- 
gent care in service. Forms and methods of design and 
construction that do not admit of ready calculation should be 
avoided; in no case should the ordinary hydraulic test be 
relied upon to guarantee the strength of parts that cannot be 
calculated with a fair degree of certainty. If such forms are 
used in any case, they ought to be tested separately to a 
pressure of two or three times the working pressure, and some 
examples of each form and size ought to be tested to destruc- 
tion. 

The boiler undergoing a hydraulic test snould be carefully 
inspected, and any notable change of shape or leakage should 



1 6 S TEA M- BOILERS. 



be investigated to discover the cause. Frequently small leaks 
that are developed during a test are stopped at once by 
calking or otherwise, but it is preferable to mark the place 
of the leak and calk after the pressure is removed. This of 
course requires another test to find out if the calking is suc- 
cessful. 

The pressure is usually applied by filling the boiler entirely 
full of water and then pumping in enough water, by hand or 
by power, to supply the leaks and develop the pressure 
required. If the pumping is done by hand, it is desirable to 
carefully remove all air from the boiler to avoid the labor of 
compressing air up to the test pressure. If the pumping is 
done by power, the saving of work is of less consequence, and 
a little air remaining in the boiler will act as a cushion, and 
lessen the shocks due to the strokes of the pump. 

New boilers are tested on the boiler-shop floor; old boilers 
are commonly tested in their settings, and in such case the 
inspection during a test is less convenient and efficient. 

It is sometimes recommended that hot water shall be used 
for testing a boiler; but there seems to be no advantage in 
so doing, as it is unequal expansion, and not merely rise of 
temperature, that sets up the unknown stresses that are so 
destructive to the boiler. Of course the use of hot water 
makes an efficient inspection during the test difficult if not 
impossible. 

When there is no other way of applying the hydraulic test 
to a boiler in its setting, the boiler may be quite filled with 
water, and then a light fire may be started in the furnace. 
The expansion of the water will develop the required pressure 
at a much less temperature than that of steam at the same 
pressure, and with less danger should the boiler fail. This 
method cannot be recommended for general use; and in case 
it is followed care must be taken not to exceed the desired 
pressure. 



STRENGTH OF BOILERS. 317 

Hydraulic Test to Destruction. — In 1888 a boiler-shell, 
made to represent a part of the shell of a gunboat boiler, was 
tested by hydraulic pressure at the Greenock Foundry,* with 
the intention of bursting it. The shell was 1 1 feet long and 
7 feet 8 T 3 g- inches mean diameter. It was made of three sec- 
tions of 19/32 plate, triple-riveted, with butt-joints and double 
cover-plates at the longitudinal joints, and lapped and double 
riveted at the ring seams. The rivets were staggered for both 
longitudinal and ring seams. The end-plates were 20/32 
thick, and stayed with through-stays and washers, spaced 14 
inches on centres. The stays were ij inches in diameter; 
the screws at the ends of the stays were 2 \ inches in diameter. 
Finally, it may be said that the shell was designed to fulfil 
the Admiralty specifications for a working pressure of 145 
pounds per square inch. The workmanship was of the same 
degree of excellence usual for boiler-work at that establish- 
ment. 

First Test. — The shell was first subjected to the working 
pressure of 145 pounds, and showed a slight alteration of form 
due to the tendency of internal pressure to give it a true cylin- 
drical form. The pressure was then raised to the Admiralty 
test pressure of 235 pounds, and then to 300 pounds without 
developing leaks. There were some minor changes of form 
due to the increase of pressure. The pressure was then 
removed and the shell returned to its original dimensions. 

Pressure was then raised to 330 pounds, when there was a 
slight leak at the manhole door. At 450 pounds pressure 
the leak at the manhole door exceeded the capacity of the 
pumps. There was also a slight leak at the corners of two 
butts. The manhole was then strengthened — no other repairs 
were made. 

Second Test. — Pressure was raised to 350 pounds and 
developed a small leak at the manhole. There were slight 

* Trans. Inst. Naval Arch., vol. xxx. p. 285. 



3i8 



STEAM-BOILERS. 



leaks at the butt-straps, which were calked at the end of the 
test. The manhole, however, leaked so that the test was 
stopped. 

Third Test. — After additional bolts were put into the 
manhole cover the pressure was raised to 350 pounds with- 
out leakage. At 360 pounds the manhole began to leak, and 
at 580 pounds the test was stopped on that account. The 
butt-straps opened visibly at the calking and leaked more 
than before. 

Fourth Test. — The butt-joints were again calked and 
additional pumps were employed. The shell was again tight 
at 350 pounds and the pressure was carried to 620 pounds, at 
which there was a good deal of leakage at the butt-straps. 
Only one or two rivets showed signs of leakage; there 
appeared to be no difference between the hand and machine 
riveting in this respect. At the pressure of 620 pounds the 
entire capacity of the pumps was required to supply the 
leakage. 

The distortion of the shell was very marked at the higher 
pressures, and increased with the pressure; thus the ends 
bulged an inch at 520 pounds, about \\ inches at 580 pounds, 
and nearly two inches at 620 pounds. The sides bulged more 
irregularly, but to the extent of nearly an inch at 620 pounds. 
The stays drew down uniformly 1/64 of an inch at 520 
pounds, 2/64 at 580 pounds, and 4/64 at 620 pounds. They 
increased in length 2^ inches at 520 pounds, 3J inches at 
580 pounds, and 3f inches at 620 pounds; this accounts for 
the bulging of the end-plates. 

The mean tensional strength of the plates from which the 
shell and butt-straps were made may be taken at 61,500 
pounds. At 620 pounds the tension on the plates between 
the rivet-holes was 57,504 pounds, or 93 \ per cent of the 
strength oi the solid plate, and there was no serious disturb- 
ance of the structure. The ring seams increased in diameter 
about \ of an inch, and the shell bulged out between them. 



STRENGTH OF BOILERS. 319 

The various portions of the boiler acted in harmony and 
showed no special weakness at any point. The butt-joints 
had the rivets spaced 5f inches on centres to give a percen- 
tage of 83.7 per cent of the plate, and this may have caused 
the leakage found there. The riveting appeared to be 
reliable at the extreme pressure reached. This test seems to 
show that a boiler will give signs of weakness long before it 
will fail. Such signs of weakness should be carefully investi- 
gated : if there is any local weakness or deterioration, repairs 
or alterations may be made ; if there are evidences of general 
deterioration, the working pressure must be reduced, or 
better, the boiler may be replaced by a new one. 

Boiler-explosions. — The great destruction of life and 
property that is liable to be caused by a violent boiler-explo- 
sion makes it imperative that the causes should be carefully 
investigated, to the end that explosions may be prevented. 

With this in view the boiler and its parts, and any wreck 
or evidence of destruction caused by the explosion should be 
left undisturbed until the scene of the explosion can be 
examined by a competent engineer. Of course if any persons 
are injured by the explosion they must be rescued and cared 
for immediately, and also any building or structure that is so 
injured as to threaten life or safety must be attended to at 
once; but it should be borne in mind that the examination by 
the engineer for the purpose of determining the cause of the 
explosion is also in the interest of humanity, since its aim is 
to avoid future explosions. All idle or simply curious per- 
sons should be excluded from the scene of the explosion, more 
especially as such persons are apt to disturb or even carry 
away things that may be of importance in the study of the 
cause and history of the explosion. If the explosion is 
accompanied by loss of life or injury to person or property, 
it will be followed by a le^al investigation in which the testi- 
mony of the engineer or engineers who have examined the 
scene of the explosion will be of prime importance, as it will 



320 



S TEA M-BOILERS. 



have a large influence in locating responsibility for the 
disaster. 

While various causes may lead to boiler-explosion, it is 
unfortunately true that by far the greater part of violent 
explosions are due to the fact that the boiler is too weak to 
endure service at the regular working pressure. A new boiler 
may be weak through defective design or workmanship; 
there can be no excuse for the explosion of a new boiler from 
weakness, and such explosions in good practice are rare. An 
old boiler is liable to become weak through local or general 
corrosion or other deterioration; this amounts to saying that 
a boiler will eventually wear out. 

The length of time that a boiler will endure service 
depends (i) on the design, (2) on the thickness of plates and 
the quality of the metal, (3) on the workmanship, (4) on the 
care given it, and (5) on the quality of the feed-water. 
Definite figures cannot be given for the life of a boiler, since 
it depends on so many things. The following table gives the 
number of years several kinds of boilers can endure regular 
service if they are properly built and cared for: 

Lancashire, low-pressure 1 5 to 20 years. 

Locomotive type, stationary 12 to 1 5 

Locomotive-boilers 8 to 12 

Vertical boilers 10 to 15 

Vertical boiler with submerged tubes 14 to 18 

Horizontal cylindrical tubular 15 to 20 

Scotch marine boiler 1 2 to 1 5 

Water-tube boiler 12 to 16 

Pipe or coil boiler 5 to 8 

By water-tube boiler is here meant a boiler with a shell 
or drum containing a considerable body of water. By pipe 
or coil boiler is meant a boiler made up of pipe and pipe- 
fittings, with a separator. 



STRENGTH OF BOILERS. 



321 



Horizontal boilers will require one, and vertical boilers two 
extra sets of tubes, before the shell is condemned. A loco- 
motive-boiler will require two extra sets of tubes, and the 
entire fire-box will be renewed once in the life of the boiler. 

If boilers are subjected to careless or ignorant abuse., they 
may be used up in a fraction of their proper time of service, 
especially if cheaply built. This will account for the numer- 
ous explosions of sawmill boilers and agricultural boilers. 

It has been pointed out that leakage is frequently a sign 
of weakness; a perversion of this idea leads to the assumption 
that a boiler is safe as long as it can be kept from leaking. 
Too many boiler-explosions have this history: The boiler, 
after long and satisfactory service, began to leak; a cheap 
man was employed to repair the boiler, the repairs consisting 
mainly of excessive calking to stop the leaks; soon after the 
repairs, perhaps the first time the boiler was fired up, it 
exploded violently. A fit conclusion of the history is to 
ascribe the explosion to some obscure cause or to carelessness 
of the attendant, if he was killed by the explosion. 

Serious injury may be caused by overheating any part of 
the heating-surface, due to low water, to defective circulation, 
or to deposits of non-conducting substance on the plates or 
tubes. The overheated member, or plates, of the boiler may 
burst or collapse, and such failure may lead to an explosion 
of the boiler, but frequently the escape of steam and water 
will check the fire and relieve the pressure on the boiler. 
Local failures are dangerous to the boiler attendants, especially 
in a confined fire-room, as on shipboard. Unless there is 
direct evidence of overheating, either from known circum- 
stances before the explosion or from signs on the boiler after 
explosion, the cause of the failure should be sought elsewhere. 

If a boiler shows signs of low water or of overheating the 
fire should be checked by any effectual means. The most 
ready way of checking the fire is to close the ash-pit doors and 
throw ashes onto the fire. If there are no ashes at hand, then 



322 S TEA M-B OIL ERS. 

fresh fuel may be used instead, since its first effect is to deaden 
the fire. There will be time for caring for, or drawing the fire 
before the fresh fuel is fairly in combustion. An attempt to 
draw the fire without first deadening it is liable to give a fierce 
combustion for a short time; moreover, more time is required 
to draw the fire. If the furnace has a dumping-grate, the fire 
may be immediately thrown into the ash-pit without waiting 
to deaden it. The damper should be left open so that if a 
rupture occurs the steam may escape up the chimney. Mean- 
while the steam made by the boiler should be disposed of by 
allowing the engine to run or by any other means, for exam- 
ple by opening the safety-valve, provided that it is merely a 
case of overheating, not accompanied by excessive pressure. 
It will probably be well to start the feed-pumps or to increase 
the supply of feed-water. Should the introduction of feed- 
water be badly arranged so that a large volume of cold water 
will be thrown onto a heated plate, it is possible that starting 
the feed-pump may cause a contraction which will start a 
rupture. 

It has been found by experiment that boiler-flues that 
have been purposely allowed to become bare and overheated 
have been saved by suddenly directing a stream of cold feed- 
water upon them, though such treatment may make them 
leak at the joints. The heat stored in such hot plates is 
insignificant as compared with the heat in the water and steam 
in the boiler. 

Excessive pressure, especially if it is enough to give good 
reason to fear an explosion, is more difficult to deal with ; the 
chances of success are less and the risks are greater than when 
the water is low, but the pressure is not excessive. If possi- 
ble the fire should be checked and the pressure relieved. The 
first may be done by throwing on ashes or cold fuel, and the 
second by running the engine at full load. It is at least 
doubtful whether starting the feed-pump will reduce the 
pressure fast enough to do much good, and on the other hand 



STRENGTH OF BOILERS. 323 

there may be cases where such action would start an explo- 
sion. It is not best to open the safety-valve, since the sudden 
opening of a large safety-valve gives a shock which may 
determine the explosion. Some explosions have been re- 
ported that occurred immediately after the safety-valve 
opened. 

A large amount of energy is stored in the steam and water 
in a boiler in the form of heat. An idea of the amount of 
energy in any given case may be obtained by a simple calcu- 
lation. Thus the cylindrical boiler shown on Plate I, at 150 
pounds pressure by the gauge, will contain 6600 pounds of 
water and 22 pounds of steam. 

The total weight of water and steam is 6622. The fractional 

22 
weight which in steam is 77— =.00332. Should the boiler ex- 
plode the mixture of water and steam would expand adiabati- 
cally to atmospheric pressure. A portion of the water would 
have vaporized. The percentage of the entire weight which is 
steam after the explosion has taken place may be found by equat- 
ing the entropy at the two points. 

Calling #1 the fractional weight which is steam at the start 
and x 2 the fractional weight at 212 ; ri and r 2 the heats of vapori- 
zation at boiler pressure and at 212 respectively, 7^ and T 2 
the absolute temperatures, and d\ and 6 2 the entropies of the 

liquid we have that ~^ + 0i=^t"~ + ^2. If we call the boiler 
pressure 165 pounds absolute 

.00332X856.9 12X9691 

365.9+459-5 + ' 535_ 459.5+2i2 + - 3l25j 

oc 2 = -15, or about 15 per cent is steam. 

The work done comes from loss of intrinsic energy and is in 
this case equal to 

6622 XrjS(qi +X!pi -q 2 -x 2 p 2 ), 



324 STEAM-BOILERS. 

where q\ and ^2 are the heats of the liquid at the two pressures 
and p\ and p 2 are the internal latent heats. Substituting values 
for these, the expression reduces to 6622 X 778(337. 7 + .00332 X 
772.9— 180.3 — .15X896. 9) = 130,000,000 foot-pounds. 

If the entire explosion took place in two seconds, work was 
developed at the rate of 120,300 horse-power. 

If a calculation is made for this same boiler, assuming that the 
boiler was "dry," or just filled with steam, the energy developed 
would be between 5 and 6 million foot-pounds instead of 130 
million. 

A person can sometimes judge as to whether the boiler was 
dry or not at the time of the explosion b™ the amount of destruc- 
tion caused by the explosion. 

The more water a boiler contains the greater the damage done 
by an explosion. 

An explosion of a boiler carrying low pressure for heating will, 
if there is a considerable amount of water in the boiler, develop a 
number of millions of foot-pounds of energy. 

Lap-seam Boilers. — It has already been mentioned that 
pressure on the inside of a cylinder tends to bend out any flat 
places and to make the shell a true circle, while pressure on the 
outside of a cylinder tends to make the cylinder collapse. Any 
flat places in such a cylinder will make the cylinder collapse at a 
much less pressure. This has been shown by experiments on 
upright boilers. The fire-box always begins to collapse at the 
seams where one part of the circle laps over the other part because 
at this spot there is a flattened area. If in the staying of the 
water-leg of a vertical boiler an extra line of screwed stay-rivets 
be put through this joint the collapsing pressure will be raised 
from 15 to 20 per cent. 

The longitudinal joint on a horizontal multitubular boiler 
comes from 2 to 6 inches above the top of the brackets support- 
ing the boiler. There is considerable stress thrown into the joint 
by the load on the brackets. The tendency of the pressure inside 
of the boiler and the tension in the shell is to pull the flattened 



STRENGTH OF BOILERS. 325 

area at the joint into a true circle. The bending takes place at 
the rivet holes. The force tending to pull the joint into a circle 
varies every time the boiler pressure changes. These repeated 
bendings may after a long period start a crack which gradually 
gets deeper and finally determnies the life of the boiler. 

Sometimes an internal inspection of the boiler may show such 
cracks, but more often the crack starts between the two plates 
where one laps over the other. A crack in this place could not 
be found either by an internal inspection or by an external inspec- 
tion. A cold-water test might show this defect if the water 
pressure was made great enough. 

A number of boiler explosions have resulted from cracks of 
this sort. 

A lap-seam boiler may wear out before this repeated bending 
action at the joint starts a crack. If the plate used was ductile 
and the workmanship was good such probably would be the case, 



CHAPTER IX. 
BOILER ACCESSORIES. 

In this chapter will be described various fittings, attach- 
ments, and accessories for steam-boilers. 

Valves are used to control and regulate the flow of fluids 
in pipes. They are variously named after their forms or uses, 
such as globe valves, angle-valves, straightway valves, and 
check-valves. 




Fig. 129. 

Globe Valves are named from the globular form of their 

cases. The case is separated into two parts by a diaphragm 

with a passage through its horizontal part, as shown in Fig. 

129. The fluid enters at the right, passes under the valve, and 

326 



BOILER ACCESSORIES. 



327 



out at the left. The valve is shut by screwing down the 
handle on the valve-spindle. A stuffing-box around the 
valve-spindle prevents leakage of fluid. In this valve the seat 



-ffl, 



J J = I \ 




5 PIPE TAP 



Fig. 130. 



is rounded, and the valve face is a ring of a peculiar composi- 
tion, let into the valve at R. When the valve is shut, this 
composition is squeezed down onto the seat and makes a 
tight joint. 

If the fluid enters the valve from the right-hand side, the 



328 



STEAM-BOILERS. 



valve-spindle may readily be packed to prevent leakage while 
the valve is closed. If the fluid entered the valve at the 
other end, it would be necessary to shut off the fluid from 
the entire pipe in order to pack the valve. 

Angle-valves. — This form of valve, shown by Fig. 130, 
has an inlet at the bottom and an outlet at one side, it may 
take the place of an elbow at a bend in piping. The valve 
is made in two parts. The upper part carries a ring of soft 
metal which forms the bearing-surface. The lower part has 
ribs or wings which enter the opening through the valve-seat 
and guide the valve to its seat. The valve-spindle has a 




Fig. 131. 



sorew at the upper end which passes through a yoke entirely 
outside of the body of the valve. 

The body of the valve is made of cast iron. The valve, 



BOILER ACCESSORIES. 



3 2 9 



valve-seat, valve-spindle, and stuffing-box follower are made 
of brass or composition. 

This form of valve is frequently used tor the stop-valve 
between the boiler and the main steam-pipe. 

Straightway or Gate Valve. — This form of valve gives 
a straight passage through the valve, and offers very little 
resistance to the flow of fluids when it is open. Fig. 131 
represents a Chapman valve, in which the valve is wedge- 





Fig. 132. 



shaped and is forced against a wedge-shaped seat. The valve- 
spindle is held at a fixed height by a collar, and draws up or 
forces down the valve to open or close it. The body of the 
valve is of cast iron ; the valve, valve-spindle, and stuffing-box 
are ot brass; the valve-seat is a soft composition. 

Fig. 132 represents a Peet valve, which has the faces of the 
valve-seats parallel. The valve itself is made in two pieces, 



33o 



STEAM-BOILERS. 



between which is a peculiar casting, U shaped at the bottom 
and with wedge-shaped lips at the top. When the valve is 
shut this casting rests on the bottom of the valve body, and 
the two halves of the valve are thrown against the parallel 
valve-seats by the wedge-shaped lips of the casting. When 
the valve is opened this casting hangs between the two halves 
of the valve by the under side of the wedge-shaped lips. 

Check-valves allow fluids to pass in one direction, but 
not in the other. Fig. 133 represents a lift check- valve; it 





Fig. 133. 



Fig. 134. 



resembles a globe valve without a valve-spindle. Fluid 
entering at the left will lift the valve and pass out at the 
right. Should the current be reversed the valve will be 
promptly closed. 

Fig. 134 represents a swing check-valve. It offers less 
resistance to the flow of fluid than the valve shown above, 
and there is less chance that foreign matter will lodge on the 
valve-seat. The valve has some looseness where it is fastened 
to the swinging arm, so that it may properly seat itself. 

A feed-pipe must always have a check-valve to keep the 
boiler-pressure from acting on tne pump, or injector, when it 
is not at work. It automatically opens to allow water to pass 
into the boiler. There should also be a stop-valve (a globe or 
gate valve) near the boiler which can be shut at will; thus 
when the check-valve shows signs of leaking the stop-valve 



BOILER ACCESSORIES. 33 1 

may be shut, and then the check-valve may be opened and 
examined. 

Safety-valves are intended to prevent the pressure oi 
steam from rising to a dangerous point. In order to accom- 
plish this, the effective opening of the valve should be suffi- 
cient to discharge all the steam that the boiler can make 
when urged to its full capacity. The effective opening is 
equal to the circumference of the valve-seat multiplied by the 
lift of the valve, if the valve-seat is flat ; if the valve-seat is 
conical, the lift should be measured at right angles to the 
seat. Then if / is the vertical lift and if a is the angle which 
the seat makes with the vertical, the effective lift is 

/ sin a, 

The lift of a safety-valve rarely exceeds i/io of an inch. 
A two-inch pop safety-valve, made by the Crosby Gauge and 
Valve Co., and tested at the laboratory of the Massachusetts 
Institute of Technology, was found to lift from 0.07 to 0.08 
of an inch. The valve had a conical seat with an angle of 
45 . The actual flow was about 95 per cent of the calculated 
flow for this valve. 

The amount of steam that a boiler can make may be 
estimated from the grate-area, the rate of combustion, and the 
evaporation per pound of coal. The first item is fixed, and 
the other two, though somewhat indefinite, may be estimated 
from the type of boiler and the conditions under which it 
works. 

For example, a factory boiler having a grate 5 feet by 6 
feet may be assumed to burn 18 pounds of coal per square 
foot of grate-surface per hour, and to evaporate 8 pounds of 
water per pound of coal. It will therefore generate 

5X6X18X8 At, 

— fin v fin =1.2 pounds of steam per second. 

The amount of steam which will be delivered by a safety* 



332 STEAM-BOILERS. 

valve may be calculated by an empirical formula proposed by 
Rankine and frequently called Napier's equation. It may be 
written 

W = aK 

70 

in which W is the weight of steam in pounds delivered per 
second, A is the effective area of discharge in square inches, 
and p is the absolute "pressure of the steam in pounds per 
square inch. 

The formula for calculating the diameter of a safety valve 
may be put into the form 

G X R X 9 = irdlp 
3600 ' 70 

where G = grate area in square feet, 

R = coal burned per sq. ft. of grate per hour, 
d = diameter of valve in inches, 
/ = lift of valve in inches, 
p = absolute pressure on a square inch, 
.95 = a multiplier determined by test, as explained on the 
preceding page, 
9 = probable actual evaporation per pound of coal. 

The expression above is for a flat-seated valve. 

For a 45-degree seat substitute .707 / for / in this formula. 

If the value d, in any case, figures out to be over 4 inches, two 
smaller valves having a total circumferential length equal to 
that of the one large valve should be used. 

A common rule requires that there shall be an area of 1/3 
of a square inch through the valve-seat for each square foot of 
grate-surface. 



BOILER ACCESSORIES. 



333 



This rule will apply only to a certain rate of coal consump- 
tion: 15 to 20 pounds per hour per square foot of grate or 130 
to 160 pounds of steam made per hour from a square foot of 
grate. 

The method, given on the preceding page, wherein the actual 
amount of steam made is considered, is the only correct method 
of calculating the size of a safety-valve. 

Lever Safety-valve. — The general arrangement and some 
of the details of a well-made safety-valve are shown by Fig. 

135- 



Co 



WEIGHT 
115 LBS. 



CENTER OF GRAVITY 
OF LEVER 

WEIGHT OF LEVER 42 LBS. 

'WEIGHT OF VALVE AND 

SPINDLE 15 LBS. 




Fig. 135- 



The body of the valve is of cast iron, and has an opening 
at one side from which the escaping steam is led out of 
the boiler-room through an escape-pipe. The valve and 
valve-seat are of brass or composition; the bearing-surface is 
at an angle of 45 with the vertical. The load is applied by 
a steel spindle, to a point beneath the bearing-surface so that 
the valve is drawn down to its seat. The spindle passes 
through a brass ring in the cover to the valve-casing. The 
load is applied by a lever with a fulcrum at A and a weight 
at D. It is steadied by guides cast on the cover of the 
casing; in the figure the valve and body are shov/n in section 
but the spindle, lever, guides and weight are shown in eleva- 
tion. 

It is important that the pins at A and B shall be loose in 
their bearings, and that the spindle shall be free where it. 



334 STEAM-BOILERS. 

passes through the top of the valve-case, so that the valve may 
not fail to rise even if the working parts are rusted a little. 

After a safety-valve has blown off it is liable to leak a 
little, and such leakage is likely to injure the bearing-surface. 
In this way safety-valves sometimes get leaky and trouble- 
some. The proper way is to regrind the valve and make it 
tight, but if the boiler attendant is careless he may try to 
stop the leak by jamming the valve on its seat. This may 
be done by hanging on extra weight, or wedging a piece of 
wood or metal against the lever. To remove temptation, it 
is well to have the guides for the lever open at the top, and 
also to cut off the lever to just the proper length so that the 
weight cannot be slid farther out. A short lever and a heavy 
weight are better, for this reason, than a lighter weight and a 
longer lever. 

In order to make a calculation of the pressure at which a 
safety-valve will blow off, we must know the diameter of the 
valve, the weight of the valve and valve-spindle, the length 
of the lever and the weight hung at its end, and the weight 
and centre of gravity of the lever. This last may be found 
by calculation, or more simply by balancing the lever on a 
knife-edge. 

In the example shown by Fig. 135 the valve has a diameter 
of 5 inches and an area of 

3.1416X 5 3 , 

*—*- 1 = 19.635 

4 

square inches, on which the steam presses. 

The valve and spindle weigh 15 pounds; this is applied 
directly at the valve. The weight of 115 pounds at the end 
of the lever, is 56 inches from the fulcrum at A. It is equiva- 
lent to a weight of 

115X56 , 
— t ±- = 1610 

4 



BOILER ACCESSORIES. 335 

pounds at the valve. The weight of the lever is 42 pounds, 
applied at the centre of gravity C 7 20 inches from the fulcrum. 
It is equivalent to a weight at the valve of 

42 X 20 

= 210 

4 

pounds. The total equivalent weight, or the load on the 
valve, is 

15 -f- 1610 + 210 = 1835 pounds. 

Since the area of the valve is- 19.635 square inches, the 
steam-pressure per square inch required to lift the valve will 
be 

1835 -f- 19.635 = 93.46 pounds. 

Problems concerning the loading of a safety-valve may be 
conveniently stated and solved by taking moments about the 
fulcrum ; that is, by multiplying each weight or force by its 
distance from the fulcrum. 

Let the weights of the valve, spindle, lever, and weight 
be represented by V, 5, L, and W. Let a be the distance of 
the weight from the fulcrum and b be the distance from the 
fulcrum to the valve, while c is the distance of the centre of 
gravity of the lever from the fulcrum. 

The moment of the weight is Wa, and the moment of the 
lever is Lc. The moment of the valve and spindle is (V-\-S)b. 
All three moments act downward, and their total effect is equal 
to their sum, 

Wa + Lc + (V+S)b. 

If the diameter of the valve is d, then the area is \nd % . 
Representing the steam-pressure above the atmosphere by/, 
the force acting on the valve is 

nd % 



3$6 STEAM-BOILERS. 

and the moment of that force is 

■ pb. 

4 F 

This moment acts upward and, when the valve lifts, will 
be equal to the total downward moment. So that the equa- 
tion for calculating the load on a lever safety-valve is 

pb = Wa + Lc + (V+ S)b. 

This equation gives for the steam-pressure at which the 
valve shown by Fig. 135 will lift 

4 [Wa + Lc+ ( V-S)b] 
P ~ nd'b 

_ 4(1 1 5 X 5 6 + 42 X 20 -f 1 5 X 4) 
''' P -' 3.1416 X 5 2 X 4 

•'• P = 93-46 pounds, 

as found by the previous calculation. 

For a second example let us find the distance at which 
the weight of the valve shown by Fig. 135 must be placed 
from the fulcrum in order that the valve will blow off at 50 
pounds above the atmosphere. 

Solving the general equation for a, we have 

nd 2 
pb—- Lc- (V+S)b 



a = 



W 

50 X A X ^— — X5 -42X20-15x4 

. a = ± . 

ii5 

\ a = 26.32 inches. 



BOILER ACCESSORIES. 337 

For a third example find the weight which should be hung 
at the end of the lever if the valve is to blow off at 30 pounds 
above the atmosphere. 

Here we have 

nd* 
pb -Lc-{V-\-S)b 

W= ± . 



30 X 4 X 3 ' 141 X 5 a - 42 X 20 - 1 5 X 4 



W 



56 



W = 26 pounds. 



These last two problems can of course be stated and 
solved much after the first manner applied to the first problem, 
but the work, which will amount in the end to the same 
thing, cannot be so well arranged nor so easily done. 

Pop Safety-valve. — A defect of the common lever 
safety-valve is that it does not close promptly when the 
steam-pressure is reduced, and it is apt to leak after it has 
returned to its seat. 

The valve shown by Fig. 136 has a groove turned in the 
flange which projects beyond the bearing-surface, and there is 
another groove between the outer edge of the valve-seat and a 
ring which is screwed onto the valve-seat. When the valve 
lifts the escaping steam is twice deflected, once by the groove 
in the valve and again by the groove at the valve-seat. The 
reaction of the steam assists the pressure of the steam on the 
under surface of the valve, and suddenly opens the valve to 
its full extent. The valve stays wide open till the steam- 
pressure in the boiler has fallen a few pounds below the blow- 
ing-off pressure, and then the valve shuts as suddenly as it 
opens. 

The ring which is screwed onto the valve-seat has a number 



338 



STEAM-BOILERS. 



of holes drilled through it to allow steam to escape from the 
groove at its upper surface. It may also be screwed up or 




Fig. 136. 

down to adjust its position; a screw at the side of the case 
clamps it when adjusted. The action of the valve is regulated 



BOILER ACCESSORIES. 339 

by the number of holes in the ring and by its vertical posi- 
tion. 

This valve is loaded by a helical spring. The thrust of 
the spring and the load on the valve is regulated by a sleeve 
which is screwed down through the top of the valve-case. It 
is of course possible to load a plain safety-valve in a similar 
way, or to load a pop-valve with a lever and weight. The 
valve is extended up in the form of a thin shell to guard the 
spring from the escaping steam. The valve-spindle is ex- 
tended through the top of the case, and may be pulled up 
by a lever when it is desired to ease the valve off from its 
seat. A drip at the lower right-hand side of the case draws 
off water which may collect in the case. 

The valve and its seat, the adjusting-ring on the seat, the 
valve-spindie, and the bearing-pieces on the spring are all 
brass. There is also a brass ring inside the shell that extends 
down from the cover and incloses the spring. There should 
be a little clearance between this brass ring and the shell on 
the valve so that the valve shall not be cramped. The entire 
valve-casing, which is made in four parts, is of cast iron. 

It is evident that the annular space between the bearing- 
surface and the edge of the groove of the valve in Fig. 136 is 
subjected to a pressure, when the valve is open, which 
depends on the rates of flow to and from this space. Some 
pop-valves depend mainly, if not wholly, on such an additional 
pressure for their action, and it is claimed by some makers 
that all pop-valves do. The closeness of regulation by a pop- 
valve may be controlled by determining the width of the an- 
nular space and by adjusting the grooved ring outside the 
valve-seat. Valves have been made with only two pounds 
for the range of pressure between opening and closing; thus, 
a pop-valve may open at 100 pounds pressure and close at 98 
pounds. 

A safety-valve should be set by trial, to blow off at the 
required pressure as shown by a correct steam-gauge. A 
safety-valve should occasionally be lifted from its seat to 



340 STEAM-BOILERS. 

insure that it is in proper condition. An unexpected opening 
of a safety-valve or continued leakage shows lack of attention 
to duty on the part of boiler attendants. While the safety- 
valve for a boiler should be able to deliver all the steam it can 
make, it may be considered that the proper function of a safety- 
valve is to give warning of excessive pressure. The safety of 
the boiler must always depend on the faithfulness and intelli- 
gence of the boiler attendants. 

The discharge of a safety-valve is often piped outside the 
boiler-room. Such pipes should be dripped to keep them free 
of water. Each safety-valve should be piped outdoors sepa- 
rately. 

Locomotive Pop Safety-valve. — A locomotive muffled pop 
safety valve, as made by the Crosby Steam Gauge & Valve Co., 
is shown by Fig. 137. The " blow down " is varied by screw- 
ing the outer muffle casing up or down, thereby varying the 
amount of opening given the four holes leading into the central 
discharge chamber. 

At A is shown a slight modification of the inner edge of the 
seat face which has been patented by Professor Miller. By this 
slight rounding of the sharp edges commonly found at this point 
in safety-valves, the discharge through the valve with the same 
lift may be increased from 10 to 15 per cent. 

Various rules have been proposed for figuring the discharge 
capacity of safety-valves. In general these rules assume either 
a definite lift or make the lift some fraction of the diameter or 
some fraction of the diameter plus a constant. 

By putting the assumed lift, or the equation for the lift in 
terms of the diameter, in the equation given on page 332, and 
at the same time by applying a proper multiplier to Napier's 
formula, a simple expression for the discharge of a safety-valve 
may be worked out in terms of the diameter and the pressure, 
all the constants being put into one factor. 

In the recent volumes of the Transactions of the A.S.M.E. 
are given the results of two series of tests on the discharge 



BOILER ACCESSORIES. 



341 




Fig. 137. 



34 2 STEAM-BOILERS. 

capacity of safety-valves, one series made by Mr. Philip G. 
Darling and another series by Prof. E. F. Miller. 

Many engineers specify valves having a 45-degree seat 
without considering that such valves must lift from their seats 
1.4 times the amount that would be required for flat-seated 
valves of the same diameter discharging the same weight of 
steam. 

This extra lift besides bringing additional stresses to the 
spring, which is already under severe stress, also adds to the 
force of the shock or blow caused by the return of the valve 
to its seat. 

The only advantage of a high lift is an increase in the dis- 
charge capacity, and this advantage is frequently more than 
offset by the disadvantages mentioned. 

Water-column. — The position of the water-level in a boiler is 
indicated either by a water-glass or by gauge-cocks or by both. 
These may be connected directly to the front end of the boiler, 
or they may be placed on a fitting known as a water -column 
or combination. Fig. 138 shows a good form of water-column. 
It is a cast-iron cylinder connected to the steam-space at the top 
and to the water-space near the bottom. The normal position 
of the water-level is near the middle. There is at the bottom 
a globular receiver into which deposits from the water may settle 
and be blown out at will. In one side of the water-column are 
brass fittings for the water-glass, which is a strong tube of 
special make. The glass tube passes through a species of 
stuffing-box in the brass fitting. The joint is made tight by 
a rubber ring which fits on the tube and is compressed by a 
follower screwed onto it. Each fitting has a valve by which 
steam may be shut off when the tube is cleaned or replaced. 
A cock at the bottom drains water from the tube; for this 
purpose the lower valve is closed and the cock is opened. 
If either valve leading to the water-glass is closed, the 
level of the water will rise in the tube. If the upper valve 
is closed, the steam in the upper part of the glass is gradu- 



BOILER ACCESSORIES. 343 

ally condensed by radiation, and is replaced by water entering 
from below. If the lower valve is closed, the condensation 
of steam from radiation will accumulate and gradually fill the 
glass. 

Gauge-glasses are very brittle and, though carefully an- 
nealed, are under considerable stress from unequal cooling. Be- 
fore a tube is put in it may be cleaned by pouring acid through 
it, or by drawing a bit of waste through on a string. A wire 
should never be forced through a glass tube, for the slightest 
scratch may start a break which will end in reducing the tube to 
small pieces. When a tube is in place it may be cleaned by 
closing the lower valve and opening the drainage-cock and allow- 
ing steam to blow through. 

When a boiler is left banked overnight the water-glass 
should be shut off, since a breakage may result in drawing the 
water in the boiler down to the level of the lower end of the 
tube. 

In addition to the water-glass, which shows at all times the 
level of the water, the water-column carries three gauge-cocks. 
One is set at the desired water-level, one a little above, and one 
a little below. Steam from the steam-space, through the upper 
gauge-cock, becomes superheated as it blows into the atmos- 
phere and looks blue. The lower cock discharges hot water 
from the water-space, which flashes into steam as it escapes, but 
it has a white color, which is very distinct from that of the jet 
from the steam- space. A good fireman occasionally tests the 
position of the water-level by using the gauges to be sure that 
the indication by the water-glass is not erroneous. Engineers 
on locomotives, and boiler attendants where very high-pressure 
steam is used, often prefer to depend entirely on the gauge- 
cocks, and dispense with the water-glass, which may be annoy- 
ing or dangerous when it breaks. 

The water-column shown by Fig. 138 has an alarm-whistle, 
which shows above the main casting, at the right. It is con- 
trolled by two floats inside the cylinder; one float at the top 



344 



STEAM-BOILERS. 



opens the valve leading to the whistle when the water-level 
is too high, the other near the bottom blows the whistle when 
the water-level is too low. 

A ribbed glass, about if inches wide and 10 to 12 inches 
long, is frequently used in place of the ordinary gauge glass. 
This glass forms the front of a metallic box coated white on the 
interior. 




WATER 
CONNECTION 



Fig. 138. 

The glass up to the water line, due to interference of light, 
appears black, and above the water line white. 

This glass makes it easy for a fireman, who is more or 
less blinded after looking at the fires, to tell where the 
water is. 

Steam-gauges. — The pressure of the steam in a boiler is 
shown by a steam-gauge constructed as shown by Figs. 139, 
140, and 141. The essential part is a flattened brass tube bent 



BOILER ACCESSORIES. 345 

into the arc of a circle as shown by Fig. 139. The section of the 
tube may be an oval, or it may have two longitudinal corrugations 
as shown by Fig. 140. 

Pressure inside of such a tube makes it bulge and tends 
to straighten it. One end is fixed and is in communication 




Fig. 139. Fig. 140. 

with the space where the pressure is to be measured. The 
other end is closed and is free to move. It is connected by 
a link to a lever which bears a circular rack in gear with a 
pinion. The motion of the free end of the tube is multiplied 
and is shown by the motion of a needle on the pinion. The 
scale on the dial is marked by trial to agree with the indica- 
tions of a mercury column or of a standard gauge. A hair- 
spring on the pinion (not shown in Fig. 139) takes up the back- 
lash of the multiplying-gear. 

The long, flexible spring-tube is liable to vibrate to an 
undue extent when the gauge is exposed to the jarring of a 
locomotive. To avoid this difficulty, two short stiffer tubes 
have their ends connected to a more effective multiplying 
device, shown by Fig. 141. The greater number of joints in 
this device makes it less sensitive than the other form. 

Since the spring-tube changes its shape if the temperature 
changes, hot steam should not be allowed to enter it. An 



346 



STEAM-BOILERS. 



inverted siphon or U tube filled with water is, therefore, inter- 
posed between the gauge and the steam from the boiler. 




Fig. 141. 
Safety-plugs, or Fusible Plugs, as shown by Fig. 142, are 
made of brass and provided with a core of fusible metal. If 
the plate into which they are screwed is in danger of over- 
heating, the fusible metal will melt and run out, and steam 
and water will blow into the furnace. If the fire is not put 
out, it will at least be checked and the attention of the fire- 
man will be attracted. 

The melting-point of fusible metals is not always certain, 
and the plugs not infrequently blow out when there is no ap- 
parent cause. On the other hand, they sometimes fail to act 
when the plate is overheated. If the plug is covered with incrus- 
tation, the fusible metal may run out without giving warning. 
The following are some of the places where a fusible plug 
is used : 

In the back head of a cylindrical tubu- 
lar boiler, about three inches above the 
top row of tubes. 

In the crown-sheet of a locomotive 
fire-box. 

In the lower tube-sheet of a vertical 
boiler; or sometimes in one of the tubes a 
Fig. 142. little above that tube-sheet. 




BOILER ACCESSORIES. 



347 



In the lower side of the upper drum of a water-tube 
boiler. 

The fusible composition has a conical form so that it can- 
not be blown out by the pressure of the steam. 

Foster Reducing-valve. — When steam is desired at a 
less pressure than that of the boiler, it is passed through a 
reducing-valve like that shown by Fig. 143. The valve H is 
held open by the spring at/, acting through the toggle-levers 




Fig. 143. 

a, until the steam-pressure in the exit-pipe B, pressing 
on the diaphragm D, is able to overcome the spring and 
close the valve. The pressure at which this may occur is 
determined by the tension of the spring, which may be 
regulated by the screw at K. It is expected that the 
valve will be drawn up so as to admit just the proper 
amount of steam to the exit-pipe B to maintain the de- 
sired pressure in it. Valves for this purpose are liable to 
work intermittently, i.e. they close till the pressure falls 



348 STEAM-BOILERS. 

below the proper point, then they open and raise the steam- 
pressure above that point. The valve is a species of throt- 
tling-valve, and therefore cannot be expected to remain tight. 
If the machinery supplied by the reducing- valve is liable to 

be injured by excessive pressure, there must be a stop-valve 
beyond the reducing-valve. The stop-valve must be closed 
when no steam is drawn, and must be used to regulate the 
supply of steam until the amount drawn exceeds the leakage 
of the reducing-valve. 

As practically all reducing-valves make use of a diaphragm, 
or a spring, they all must give out after a certain number of vibra- 
tions of the spring or diaphragm. When a reducing-valve gives 
out there is invariably full pressure established beyond the reduc- 
ing-valve. A safety-valve large enough to take care of the 
capacity of the pipe should be placed beyond the reducing-valve. 

If high-pressure and low-pressure boilers deliver into one 
main there must be on the low-pressure main safety-valves large 
enough to take care of all the steam made by the high-pressure 
boilers. 

The Damper-regulator, shown by Fig. 144, places the 
damper in the flue leading to the chimney under the control 
of the steam-pressure, so that if the pressure of the steam falls, 
the damper is opened wider to quicken the fire. The pressure 
of the steam in the boiler is communicated through the pipe a 
to the lower surface of a diaphragm, and lifts the loaded lever b, 
which stands half-way between the stops at the middle of its 
length when the steam-pressure is at the proper point. Should 
the steam-pressure rise above the proper point, it raises the lever 
and opens a small piston-valve at c, and water from a hydrant 
flows into d and presses on a piston which lifts the weights at e 
and so shuts the damper. The weighted head e of the piston is 
connected by a chain to the lever/, and closes the valve c as it 
rises, and so shuts off the water from the hydrant. 

If the pressure in the boiler drops the lever b as it descends 



BOILER ACCESSORIES. 



349 



pulls down the piston-valve in c far enough to open a dicsharge- 
port, which allows the water under the piston in d to flow to waste. 
The weights at e are made heavy enough to overhaul the 
damper and to overcome the piston friction in d. 




fl m ^ "* m-f 



Fig. 



144. 



The diameter of the brass pipe d is fixed by the water-pressure 
available for working the regulator. 

Should the water-pressure fail, the regulator would not operate 
and the damper would be held open. 

Oftentimes damper-regulators are supplied with water from 
the fire-tanks located on the roofs of many of our factories. 

A regulator of the same form attached to a throttle-valve 



35° 



STEAM-BOILERS. 



acts as a reducing- valve, and regulates the pressure below the 
valve with a variation of less than one pound. Fig. 145 shows 

the steam-valve used when the 
Locke regulator acts as a reducing- 
valve. The valve is a double 
valve which is nearly balanced, 
but with a slight tendency to rise 
under steam-pressure, as the lower 
valve is the larger. The cylin- 
drical part of the valve is cut into 
V notches, so that the supply of 
steam is regulated to a nicety when 
the valve is partially open. The 
cylindrical portion of the valve 
protects the valve-seat and the 
valve-face so that the valve may remain tight when closed. 

Steam-traps. — The object of a steam-trap is to drain con- 
densed water from steam-pipes without allowing steam to escape. 
As a rule a trap is placed below the pipe to be drained so that 
the drip from the pipe will run into it. Some traps that return 
the condensed water to the boiler do not conform to this rule. 

Some traps, such as the McDaniels, the Baird, and the 
Walworth, have a valve under the control of a float, which 
will allow water to pass but not steam. 




Fig. 145. 




Fig. 146. 
The McDaniels trap is shown by Fig. 146. The drip 
enters at C and escapes through the exit at E when the valve 



BOILER ACCESSORIES. 



351 



G is open. This valve is raised by the spherical float when 
the water rises to a sufficient height. When the water is 
drained from the pipe served by the trap, the water-level in 
the trap falls and the valve G is closed. D is a counter- 
weight to balance the weight of the spherical float. The 
valve at G can be opened by screwing down the screw at A 



r _ ■-■^% 




Fig. 147. 




Fig. 148. 
on to the counterweight. The trap can be emptied through 
the valve at F. 

The Baird trap, Fig. 147, has a spherical float D which 



35 2 



STEAM-BOILERS, 




controls a piston-valve at J. The inlet is at C, and the outlet 
at /. The screws A and B allow the valve J to be opened or 
closed by hand. 

The Walworth trap (Fig. 148) has a floating bucket into 
which the drip overflows after the outer case is partially- 
rilled. When the bucket sinks it opens a passage through 
the central spindle, and the water in the bucket is driven out 
through this spindle. The hand-wheel and screw at the top 
control a valve which is closed when the trap is working. 

The Flynn trap (Fig. 149) depends for its action on a head 
of water acting on a flexible diaphragm. Water may enter 
at the top or the bottom at ori- 
fices marked A. It fills the pipe 
B and the globe C as high as 
the end of the pipe E, and pro- 
duces a pressure of about a 
pound per square inch on the 
under side of the diaphragm at 
D. The spring at G produces 
a pressure of about half a pound 
per square inch on the upper 
side of the diaphragm. Conse- 
quently the valve leading from 
the chamber F to the escape- 
pipe H is closed so long as the 
pipe E remains empty. But 
when the water overflows the 
top of the pipe E and fills the 
chamber F, the water- pressure 
on top of the diaphragm will be 
the same as that on the bottom, 
and the spring at G will open 
the valve and allow water to 
escape. If the supply of water Fig. 149. 

at A ceases, the pipe E will be emptied and the valve will be 
closed under the influence of the pressure on the under side 




BOILER ACCESSORIES. 



353 




OUTLET 

Fig, 150. 



In the trap as actually constructed the 
pipe E is about 28 inches long ; in 
the figure it is made shorter in 
proportion. 

The Curtis trap (Fig. 150) has 
an expansion-chamber at C which 
JU inlet is closed by a diaphragm A at the 
bottom, and is filled with a very 
volatile fluid. So long as the ex- 
pansion-chamber is immersed in 
water the pressure of the fluid on 
the diaphragm is balanced by the 
spring on the valve-spindle B. If 
the water is drained away and the 
chamber is exposed to the temper- 
ature of steam (212 F. or more), the fluid vaporizes and 
exerts enough pressure on the diaphragm to compress the 
spring and close the exit-valve. 

Return Steam-trap. — The traps thus far considered usu- 
ally discharge against the pressure of the atmosphere. They 
may discharge into a closed tank against a pressure that is higher 
than the atmosphere, but in all cases the pressure in the pipes 
drained by the trap must be higher than the discharge-pressure. 
Return steam-traps are arranged to discharge directly into the 
boiler. 

The Bundy return-trap, shown by Fig. 151, is set three feet 
or more above the water-line in the boiler. It is so made that 
it is first opened to the pipe to be drained, and fills up 
under the pressure in that pipe. It is then put in commu- 
nication with the steam-space and with the water-space of 
the boiler, and the water previously collected drains into the 
boiler. 

The trap consists of a pear-shaped receptacle or closed 
bowl, hung on trunnions, through which the bowl is filled and 
emptied. When empty the bowl is raised by a weight and 
lever; when filled with water it Overbalances the weight and 



354 



STEAM-BOILERS. 



falls. The ring around the bowl limits the motion. The 
condensed water from the pipe or system of pipes to be 
drained enters the trap through the check-valve B, which pre- 
vents water from flowing back from the trap into the pipe to 
be drained. The trap is emptied through the check-valve A, 
which prevents water from the boiler from flowing into the 




Fig. i 5i . 
trap. At C is a valve under the control of the trap, which 
receives steam by a special pipe from the boiler. When the 
trap is empty and is lifted by the weight and lever, the valve 
C is thrown down and is shut ; water then flows in through 
the valve B from the pipe to be drained, and air escapes from 
an air-valve below C> which is open in this position of the 
trap. A check-valve on the" air-pipe prevents air from en- 



BOILER ACCESSORIES. 



355 



tering the trap if a vacuum happens to be formed in it. When 

the bowl is filled it falls and opens the steam-valve C, and 

steam enters the bowl through a curved pipe shown in Fig. 

151. The pressure in the bowl is now equal to that in the 

boiler, and the water collected flows into the boiler by gravity. 

Separators. — If steam is carried to a distance in pipes, a 

considerable amount of water of conden. 
I 



^J sation accumulates. It is undesirable to 
have this water delivered to a steam- 
engine in any case, but if the water ac- 
cumulates in a pocket or a sag in the 
piping, it may come along with the steam 
in a body whenever there is a sudden 
change of steam-pressure, and then the 
engine will be in danger of injury. 

A good way of removing such water 
is to allow the steam to come to rest 
in a steam-drum of suitable size, from 
which the water is drained by a steam- 
trap ; the steam meanwhile may flow from 
a pipe at the top of the drum. A small 
steam-drum used as separator is likely 
to fail, from the fact that the steam does 
not come to rest, or because the entering 
and leaving currents of steam are not 
properly separated. 

The Stratton separator, shown by 
Fig. 152, brings in the steam at one side 
of a cylinder, with a whirling motion 
that throws the water onto the side of 




^ ^4,^,^r 



Fig. 152. 
the cylinder; dry steam escapes through a pipe in the middle. 

A good steam-separator will remove all but one or two 
per cent of moisture from steam, even though the entering 
steam is very wet. 

Attention has already been called to the use of separators 



356 



STEAM-BOILERS. 



with some forms of water-tube boilers which do not have a 
sufficient free water-surface for the disengagement of steam. 

The three separators shown by Figs. 153, 154, and 155 may 
be used on the steam-pipe to separate water from the steam, 
or on the exhaust-pipe of an engine fco collect the water and oil. 






Fig. i 53 . 

Fig. 153 represents the Curtis baffle-plate separator. The 
entering steam is divided into three portions, which flow as shown 
by the arrows. 

Water or oil coming in contact with the plates adheres to the 
plates and is collected in the space at the bottom. 

The Triumph separator, shown by Fig. 154, removes oil or 
water by centrifugal action and by a settling-chamber. The 
direction of flow is shown by the various arrows. 

Fig. 155 illustrates the Detroit separator. The steam is 
directed against a corrugated annular plate to which water and 



BOIL ER A CCESSORIES. 



357 



oil adheres. A settling-chamber in the shape of an enlargement of 
the casting allows floating particles to be deposited by gravity. 

Tests made with these separators connected to the exhaust- 
pipe of an engine have shown that by their use 80 per cent of the 
cylinder oil used in the engine may be taken out of the exhaust. 




Fig. 155. 

Most of this oil is mixed with water in such a way that it cannot 
be separated from the water. 

Oil-filters. — If exhaust steam is used for heating and the 
condensation in the system is returned as feed-water to the boiler 
it is of great importance that this water should be free from oil. 

An oil-separator will take out 80 per cent of the oil. The 
greater part of the 20 per cent remaining may be taken out by 
a straw-filter. 

The returns from the heating system are passed through a 
box about 8 feet long and 2 feet square in section, open at the 
top. There are partitions across the box so that the water enter, 
ing at one end flows over one partition and under the next, over 
the third, and so on. 

The entire box is filled full of hay or straw. Water is taken 



358 



STEAM-BOILERS. 



into the feed-pump from the opposite end of the box. If this 
straw is changed once in two weeks, or oftener if necessary, not 
enough oil will get into the boilers to cause any trouble. 

Feed-water Heaters. — The feed-water supplied to a boiler 
SAFETY 
VALVE 



BLOW 



* FEED TO 

BOILER 



EXHAUST 




FEED FROM 
PUMP 



m^mMZmjgmS&S^g^^S^gm^ 



u 

MUD BLOW-OFF 

Fig. 156. 

may be heated up to the temperature of the exhaust-steam by 
passing it through a feed-water heater. Feed-water heaters 
are sometimes made open, i.e., the steam from the engine 



BOILER ACCESSORIES. 



359 



mingles with and heats the feed-water. Such heaters have 
the disadvantage that the oil from the engine is carried into 
the boiler. 

A closed feed-water heater resembles a surface condenser, 
and as the steam and water do not mingle, there is no danger 
of carrying oil from the engine into the boiler. The Wain- 
wright heater, shown by Fig. 156, has the heating-surface of 
corrugated copper or brass tubes, of peculiar make, to allow 
for expansion. The steam from the engine passes around 
the tubes and the feed-water passes through the tubes. 

The Berryman feed-water heater, shown by Fig. 157. is 
arranged to have the exhaust-steam pass 
through a series of inverted U tubes, 
around which the feed-water circulates. 
Live-steam feed-water heaters take 
steam from the boiler to raise the tem- 
perature of the feed-water up to, or 
nearly to, the temperature in the boiler. 
The principal advantage appears to be 
that unequal contraction, due to the in- 
troduction of cold water, is avoided. It 
is claimed that with some forms of 
boilers a better circulation is obtained 
by aid of such a heater. 

The use of a feed-water heater for 
removing lime-salts from feed-water has 
been discussed on page no, and an ex- 
ample of such a feed-water heater wai: 
illustrated in connection therewith. 

Feed-pipes. — The temperature of 
the feed-water is usually much below 
the temperature in the boiler. It thus 
becomes essential to so locate the inlet, 
and to so distribute the water, that un- 
due local contractions may not occur; this is of special im- 




360 STEAM-BOILERS, 

portance when the supply is intermittent. The feed-pipe for 
the cylindrical tubular boiler, shown by Plate I, enters che shell 
near the water-line, through the front head. It is carried 
along one side of the boiler for about three fourths of its length, 
and then is carried across over the tubes and opens downward. 
A feed-pipe is often perforated to give a better distribution of 
the feed-water. 

The shell is reinforced by a piece of plate riveted on the 
outside, where the feed-pipe enters the boiler. The end of 
the pipe has a long thread cut on it, so that it can be secured 
through the reinforcing-plate and the boiler-shell, and may 
then receive a pipe-coupling which connects it to the continu- 
ation of the feed-pipe inside. 

Sometimes the feed-water is delivered to an open trough 
inside the boiler, from which it overflows in a thin sheet. 
Or a perforated pipe may deliver the water in form of spray 
in the steam-space. Either method has the advantage that the 
water comes in contact with steam and is heated before it 
mingles with the water in the boiler. There is the disadvan- 
tage that the steam-pressure may fall off when the feed-water 
is turned on or is increased. 

It has already been pointed out that the feed-pipe should 
have a globe valve near the boiler, and a check-valve between 
the globe valve and the feed-pump. 

Feed-pumps. — Boilers are commonly fed by a small direct- 
acting steam-pump placed in the boiler-room. The steam- 
consumption per horse-power per hour of such pumps is very 
large, and yet the total steam used is insignificant. They are 
cheap and effective, and easily regulated. 

If the boiler-pressure is over 100 pounds an outside packed 
plunger is preferable to a piston-pump. 

The pump should be of the duplex type and the plungers at 
the water end should be covered with a composition or brass 
sleeve. A section through the water end of such a pump is 
shown by Fig. 158. 



BOILER ACCESSORIES. 



361 



Power pumps driven from a large engine are more econom- 
ical, provided their speed can be regulated; they not infre- 
quently are arranged to pump a larger quantity than required 
for feeding the boiler, the excess being allowed to flow back to 
the suction side of the pump through a relief- valve. 

When one pump supplies several boilers, a series of diffi- 
culties is liable to arise. First, if the boilers are fed singly in 
rotation, the large intermittent supply of feed-water is likely to 
give rise to local contraction and the water-level in the boiler 
fluctuates; there is liability that the water-level will fall too 




Fig. 158. 



low, endangering the heating-surface, or there may be excessive 
priming when the water-level is high. It appears advisable 
that the feed should be delivered to all the boilers simultaneously, 
the supply to each boiler being regulated by its stop-valve; 
each branch pipe to a particular boiler should be provided with 
its own check-valve, and the water-level and rate of feeding of 
each boiler must be carefully watched by the fireman, or by a 
water-tender if there are many boilers. 

Injectors. — An injector is conveniently used for feeding a 
boiler if the feed-water is not too hot; it has the incidental ad- 
vantage that it heats the water as it feeds it into the boiler. An 



362 



STEAM-BOILERS. 



injector should be connected up with unions/so that it may readily 
be taken down for inspection. At sea an injector is commonly 
used when the boilers are fed from the sea or from a supply- tank. 
Every boiler should have two independent sources of supply 
of feed-water, so that there may be some resource if the usual 
supply gives out. There may be two pumps, or a pump and an 
injector. A locomotive usually has two injectors. 




Fig. 159. 



As the amount of water delivered by an injector can be 
varied only by a small amount, and as an injector has to be large 
enough to supply a boiler at the time of maximum demand, it 
follows that under the ordinary working conditions of the boiler 
the injector must be used intermittently. 

Fig. 159 illustrates a Koerting injector. This injector has 
two sets of tubes; the lower or lifting-tube and the upper or 
forcing-tube. 

After opening the steam-valve in the pipe S, the injector is 
started by pulling the handle about ij inches to the left. This 
uncovers the lower steam-nozzle or lifting-nozzle. 



BOILER ACCESSORIES. 363 

As soon as water appears at the overflow 0, the handle is 
pulled back as far as it will go. This, after opening the lower 
steam-nozzle to its full amount, opens the upper steam-nozzle, 
and at the same time pushes down the overflow-valve through 
a link running along the side of the injector. It will be noticed 
that the water must meet with considerable resistance in passing 
through the various passages in the injector. 

Power Pumps. — Where there is more exhaust steam from 
the auxiliaries than is needed to heat the feed-water, there is no 
reason why a steam pump should be used to feed the boilers. 
A power pump driven by the main engine or driven by a motor 
supplied with current from the main engine will, under such 
conditions, be much more economical. 

A belt-driven plunger pump is illustrated by Fig. 160. It 
is evident that in order to change the amount of water sent to 
the boiler by one of these pumps, either the speed must be varied, 
which may be accomplished by driving through a variable 
speed motor, or a by-pass must be connected so that some of 
the discharge water may be taken back into the suction. 

Where a pump is run at constant speed, and the regulation 
of the quantity of water fed to the boilers is accomplished through 
a by-pass, the amount of power required to drive the pump is 
the same whether the by-pass is opened much or little. 

In some plants three pumps are installed, the capacity of the 
three being equal to the maximum demand for feed-water ever 
made. When the load is light one pump only is run, and the 
quantity of water delivered by it to the boiler regulated by the 
by-pass; as the load increases two pumps are put on, one run- 
ning with the by-pass closed and the other with the by-pass 
closed as much as may be required. 

There must always be an auxiliary feed pump, which should 
invariably be steam driven. 

Turbine Driven Stage-Centrifugal Feed Pump. — The pressure 
obtained in a single-stage centrifugal pump depends upon the 
linear speed of the outer ends of the impellers. 



364 



STEAM-BOILERS. 




BOILER ACCESSORIES. 



365 



If a steam turbine, running at speeds between 2000 and 4000 
revolutions per minute, be used to drive the impeller of such a 
pump, considerable centrifugal force will be developed even with 
a small diameter of impeller. 

By delivering water from the first stage of the centrifugal 
under 40 pounds pressure, which we will assume was the pressure 
developed in that stage, into the suction of the second stage, the 
second stage is put under 40 pounds pressure to start with, and 
the centrifugal force developed by the impeller in this stage 
adds 40 pounds, making the pressure at delivery from the second 
stage 80 pounds. 




Fig. 161. 

By adding a sufficient number of stages, water may be 
pumped against 250 pounds pressure. 

There are no discharge valves in this type of pump, and there 
is no suction valve when the water comes to the pump under 
a head. 

There is no danger of getting an excessive pressure in the 
piping should the delivery valve be closed, as the water after 
reaching a certain pressure, depending on the speed of the tur- 
bine driving the pump, would be carried around with the im- 
pellers in the pump. 

The pump is sure and reliable as a feed pump. 



366 



STEAM-BOILERS. 




BOILER ACCESSORIES. 367 

Fig. 161 shows a side view of a turbine and pump, the pump 
being at the left-hand end. Fig. 162 is a section taken through 
the stage centrifugal pump. 

The water enters the pump, Fig. 161, from beneath, and is 
delivered at the opposite end of the pump. 

In Fig. 162 water enters at the centre on the left-hand side, 
and its path through the four stages is shown clearly by the 
arrows. 

To increase the efficiency diffuser rings are placed in each 
stage between the impeller and the outer chamber. 

These rings are generally fixed, but in some few cases they 
have been made movable. 

Blow-off Pipe. — The blow-off pipe draws from the lowest 
part of the boiler, or from some place where sediment may be 
expected to collect. On the blow-off pipe there is a cock or a 
valve which is opened to blow out water from the boiler. Some- 
times there are both a cock and a valve. A cock has the dis- 
advantage that it may give trouble by sticking; a valve may 
leak and the leak may not be detected. 

The pipe should be carried beyond the cock, so that the 
attendant is not liable to be splashed with hot water, but the 
pipe should end in the boiler-room or where discharge through 
the pipe on account of a leaky cock or valve may be sure to 
attract attention. Each individual boiler should have its own 
blow-off pipe. 

The blow-off pipe where it passes through the back connec- 
tion is covered with magnesia, asbestos, or fire-brick. In spite 
of this protection the blow-off pipe may burn off. The device 
shown by Fig. 163 is used to overcome this difficulty. When 
the blow-off cock is shut and the valve on the vertical branch 
is open, there is a continuous circulation of water which keeps 
the pipe from burning. The valve on the vertical branch is 
closed before the blow-off cock is opened. 

If a blow-off pipe burns off and water begins to escape, 
the feed-pump should be run at full capacity to keep water in 



3 68 



STEAM-BOILERS. 



the boiler and guard the plates from burning, if that is possible. 
The fire should then be checked by throwing on wet ashes or 
by other means, unless escape of steam from the break in the 
blow-off pipe prevents. 

Blow-off Tanks. Boilers located in the thickly settled dis- 
tricts of a city are obliged to discharge the water coming from 
the blow-off pipe into the city sewer. 

In most cities one is not allowed to discharge hot water into 
the sewer as it disintegrates the tile sewer pipe and causes other 
troubles. 




Fig. 163. 



Tn such cases a blow-off tank is placed at a sufficient height 
over the boiler so that it will drain by gravity into the sewer. 

This tank is made of steel plate, and is provided with a 
manhole, an open vent pipe, and with inlet and outlet pipes 
connecting with the blow-off pipe and with the sewer. There 
should be a valve in the outlet pipe. 

The size of the tank determines the amount of water which 
can be blown out at one time. 

After the water collected in the tank has cooled sufficiently 
the outlet valve is opened and the water discharged into the 
sewer. 



BOILER ACCESSORIES. 



369 



Piping" to carry steam from a boiler to an engine, for 
heating buildings- and for other purposes is too important to 
be considered as accessory to the boiler. A iew remarks, how- 
ever, may not be out of place. 

The coefficient of expansion of steel pipe is .0000065. This 
means that for each degree increase in temperature the pipe 
expands this fraction of its length. 

Thus a pipe at 70 F. measures 100 feet. What will be the 
expansion of this pipe if used to carry superheated steam at 165 
pounds absolute pressure with 150 superheat? 

At 165 pounds absolute the temperature is found from the 




0-Six% holes 

h'balanced expansion joint 




Fig. k 



tables to be 365°.o. F.; add 150 to this, giving 5i5°.o. as the tem- 
perature of the steam. The increase of temperature is 515.9 — 70 

or 445°-9- 

445°.oX.ooooo65Xioo'Xi2" = 3.48' 

the expansion in the 100 feet. 

In a long line of high-pressure piping where the expansion is 
6 or more inches, the expansion may be taken up in an expansion- 
joint like that shown by Fig. 164. The flanges at either end are 
connected to the pipe. 



370 STEAM-BOILERS. 

The drawing needs no explanation. 

An expansion- joint, like Fig. 164, is in use on a 20-inch pipe 
at the Merrimack Mills at Lowell, Mass. The following figures 
on expansion were obtained by the chief engineer: 

Length of 20-inch and 16-inch pipe, 277 feet 8 inches. 
Temperature of outside air, 56 F. 
Expansion of the pipe at 50 pounds gauge, 4 Jf inches. 
At 100 pounds gauge, 5|| inches. At 150 pounds gauge, 
6|f inches. 

In long runs of pipe not over 6 inches in diameter, the expan- 
sion may be allowed for by screwed fittings, as shown by Fig. 165. 




• Fig. 165. 

The pipes shown broken are anchored at either end. The 
length of the pieces running at right angles depends upon the 
amount of expansion to be taken care of. 

As arranged there is no chance to pocket water in the expan- 
sion-joint. A drip should be provided at the end of the pipe 
bringing steam into the joint. 

A common way of allowing for expansion is illustrated by 
Fig. 166, which shows the connection from a boiler to the main 
steam-pipe. When the main steam-pipe expands or contracts, 
the short nipple between it and the angle-valve turns a little at 
one or at both ends; in like manner the vertical pipe turns a 
little at the nozzle or at the elbow. The motion is so small and 
so distributed as not to give any trouble unless the expansion to 
be provided for is very large. 



BOILER ACCESSORIES. 



37 1 



Fig. 1 66 is so arranged that there is no space where water 
can collect when the boiler is shut off from the main steam- 
pipe. If the stop-valve were in the vertical pipe, as is some- 
times the case, then the pipe over the valve would fill up with 
water when the boiler is shut off, and that water would be 



O 




A 



Fig. 166. 



suddenly blown into the steam-main when the stop-vaive is 
next opened. A pipe so situated should always have a drip- 
pipe to draw off condensed water before the valve is opened. 
As a special example we may mention the pipe leading to an 
engine, which always has a drip-pipe above the throttle-valve. 
Pipes that are likely to be troubled by condensation should 
be continuously drained by a steam-trap. 

Horizontal pipes are sometimes arranged so that water may 
collect in them, due to a sag in the pipe or to the fact that 
they do not properly drain through a side branch. Though 
the water may lie quiet in such a pocket while the draught of 
steam is steady, a sudden increase in the velocity of the steam, 
or a rapid opening of the valve supplying steam to the pipe, 
will sweep the water up and carry it along with the steam. The 
danger from the inrush of water to an engine is readily seen, 
but it is not so well known that the water thus violently thrown 



372 STEAM-BOILERS. 

against elbows and other fittings give rise to leaks, if it does not 
burst the fittings. It is to be remembered that steam offers 
little or no resistance to the movement of water in a pipe, as it 
is readily condensed either from a slight increase of pressure 
or by mingling with colder water. Again, water at the temper- 
ature corresponding with the pressure easily separates, forming 
bubbles of steam, which as easily collapse, and the shock of 
impact of the water gives rise to pressures that search out 
all weak places in the pipe, even at some distance. 

Steam-piping should be pitched in the direction of the flow 
of the steam sufficiently to drain out the condensation. 

Should a large pipe be connected to one of smaller diameter, 
the bottom of the inside of the pipes must be kept on the same 
level. For this purpose eccentric flanges and tees with eccentric 
outlets may be used. 

To-day nearly all of the high-pressure piping is put up with 
elbows made of bent pipe instead of cast-iron or gun-iron flanged 
fittings. The bent pipe, by giving, allows for expansion, and it 
also reduces the friction loss in passing through the quarter turn. 
The radius of the bends is commonly made equal to five diam- 
eters of the pipe. 

To get some idea as to the stiffness of these bent pipes the 
following tests on bent pipes were made at the Massachusetts 
Institute of Technology by two seniors under the direction of one 
of the writers: 

The figures marked Pipes Nos. 1-9 give the size and weights. 
The load was applied at the points marked by the arrows, and 
deflections were measured at points indicated by the dash and 
dot lines. 

Fig. 167 illustrates the best practice in connecting a boiler to 
the main. The pipe is given a slight pitch towards the main. 
There are two straight-way valves with advancing stems and a 
blanked tee in the line. The three may be bolted together. 
The valve operated by the chain has a by-pass (not shown). 

If a boiler is piped to the main in this way there is no danger 



BOILER ACCESSORIES. 



373 




m 

n fi-cr 



fa 



«fe^ 




Weight = 552 lbs. Outeide dia. 6.625 Inside dia. 6.065 





Weight =133 lbs, Outside dia.S.SQQ, Inside dia. 3.067 





374 



STEAM-BOILERS. 



PIPE No. i. 
Outer dia. 5". Inner dia. 4.25" 



PIPE No. 2. 
Outer dia. 6.625". Inner dia. 6.065' 





Total Motion in Inches. 


Load, 
Pounds. 






At Outer 


At Inner 




Line. 


Line. 


200 


.060 


.025 


400 


.125 


.050 


600 


.185 


.076 


800 


.250 


I05 


1000 


•3" 


133 


1200 


.372 


.160 


1400 


-435 


.185 


1600 


.499 


.213 


1800 


.561 


.240 


2000 


.625 


.265 





Total Motion in Tnches. 


Load, 
Pounds. 




At Outer 


At Middle 


At Inner 




Line. 


Line. 


Line. 


600 


.29 


.16 


.08 


1200 


-58 


-31 


.16 


1800 


.87 


•45 


-23 


2400 


1. 16 


.61 


31 


3000 


1.50 


.78 


■39 


3600 


1.88 


.96 


.48 



PIPE No. 3. 

Outer dia. 6.625". Inner dia. 6.065' 



Load, 
Pounds. 


Total Motion in Inches. 


At Outer 
Line. 


At Second 
Line. 


At Third 
Line. 


At Inner 
Line. 


200 

400 

600 

800 

1000 

1200 

1400 


1.20 
2.35 

3-55 
4.70 
5-9° 
7-3° 
9-i5 


0.83 
1-65 
2-45 
3-30 
4-15 
5.20 
6.50 


0.50 
0.97 
1-45 
i-95 
2-55 
3.20 
4.00 


0.17 

0-34 
0.80 
O.67 
0.86 
1. 10 
1-5° 



PIPE No 4. 
Out. dia. 6.625". In. dia. 6.025' 





Total Motion 
in Inches. 


Load, 
Pounds. 




At Outer 
Line. 


At Inner 
Line. 


IOOO 


.050 


-OI5 


2000 


.107 


.030 


3000 
4000 
5000 
6000 


.167 

• 230 
-293 
-365 


-045 
.060 
.080 
.100 


7000 


-442 


.123 


8000 
8500 


.542 
.603 


• *55 
.174 



PIPE No. 5. 
Outer dia. 5.563." Inner dia. 5.045' 



Load, 
Pounds. 


Total Motion in Inches. 


At Outer 
Line. 


At Inner 
Line. 


IOOO 

2000 
3000 
35°° 


.205 
.407 
.612 
.740 


.058 

•"5 

.177 
.216 



BOILER ACCESSORIES. 



375 



PIPE No. 6. 
Outer dia. 8.62". Inner dia. 7.62". 



PIPE No. 7. 
Out. dia. 7.625". In. dia. 7 023' 





Total Motion in I 


nches. 


Load, 














Pounds. 










At Outer 


At Middle 


At Inner 




Line. 


Line. 


Line. 


1000 


•175 


.108 


050 


2000 


•345 


217 


. 100 


3000 


.516 


•3 2 4 


.151 


4000 


•695 


-435 


.205 


5 coo 


.860 


•542 


.255 


6000 


I.032 


.652 


■3°7 


7000 


I 206 


.761 


.360 


8000 


1 375 


.872 


.410 


8500 


1.463 


-932 


.440 



PIPE No. 8. 
Out. dia. 3.500". In. dia. 3.067". 



Load, 
Pounds. 


lotal Motion in Inches. 


At Outer 
Line. 


At Middle 
Line. 


At Inner 
Line. 


IOO 
200 
300 
400 


,820 
I.620 
2.420 
3.280 


-441 

.880 

1.320 

1. 912 


-1 24 
.248 
.380 
.500 





Total Motion 




in Inches. 


Load , 




Pounds. 








At Outer 


At Inner 




Line. 


Line. 


IOOO 


.182 


.080 


2000 


390 


. 160 


3000 


.628 


• 252 


4000 


.892 


.366 


5000 


1.225 


•5IO 


5500 


I.480 


.618 



PIPE No. 9. 
Out. dia. 3.500". In. dia. 3.067' 





Total Motion in Inches. 


Load, 
Pounds. 






At Outer 
Line. 


At Inner 
Line. 


200 


.158 


■037 


400 
600 




3 11 
466 


.071 
. 106 


800 




620 


. 142 


IOOO 




775 


.178 


1200 




95° 


.228 


1400 


I 


215 


319 




Fig. 167. 

in going inside the boiler even though there may be 200 pounds 
pressure in the main. By shutting both valves and uncovering 



376 STEAM-BOILERS. 

the outlet on the blanked tee there is no possibility of steam 
leaking back into the boiler. 

The outlet of the tee may be on the side or on the bottom. 
Piping must be anchored at some point. Generally there 
must be an anchorage near the engine. Each system of piping 
has to be considered by itself, and no general rule can be given. 
A simple form of anchor is shown by Fig. 168. If a pipe 
passes through a brick wall a clamp may be made to fasten to the 
pipe and to bear against the wall. 

Fig. 169 shows a method used in supporting large pipes. The 
top roller is generally omitted. 

Small piping, up to 8 or 10 inches, is frequently hung by 
rings. 

Figs. 170, 171, and 172 show three of the forms of flanged 
joint used on high-pressure piping. Fig. 172 is known as the 
Van Stone joint. 

Bursting Pressure of Extra Heavy Flanged Fittings, — 
— An investigation as to the strength of fittings was made by the 
Crane Company and the results of their tests published in The 
Valve World of Nov., 1907. From their tests they deduced the 
following formula: 

T = thickness of metal; 
Z> = inside diameter; 
B = bursting point; 

£ = 65 per cent of tensile strength of the metal up to 12 
inches diameter and 60 per cent for sizes over 12 
inches diameter. 



T 
pXS=B. 



For working pressure divide B by a factor of from 4 to 8 as desired. 
Vibration of Steam-pipes. — Steam pipes-connected to high- 
speed engines seldom vibrate much. Pipes leading to slow- 
speed engines often vibrate badly. 



BOILER ACCESSORIES. 



377 




Fig. 1 68. 




Fig. 169. 




Fig. 170. 





Fig. 171. 



Fig. 172. 



378 STEAM-BOILERS. 

An engine, rigid on its foundation, may set up vibrations in a 
pipe through pulsations caused by the checking of the velocity of 
the steam at cut-off. Such vibrations are most apt to oocur in 
pipes which are amply large for the engine. 

In most cases of vibration, if the stop-valve on the boiler is 
closed so as to make a slight drop in pressure at the engine, 2 
or 3 pounds, the vibration will cease. A large drum placed close 
to the engine with a throttling-valve in the steam-pipe entering 
the drum will accomplish the same result. The valve close to 
the drum will then be used to stop the vibration 

Area of Steam-pipe. — In order that the loss of pressure in a 
steam-pipe due to friction may not be excessive, it is customary 
to limit the velocity to 5000 or 6000 feet per minute where 
steam is taken intermittently, as, for example, in the pipe sup- 
plying a slow-speed reciprocating engine. 

Pipes for steam turbines and for high-speed reciprocating 
engines may, on account of the steady flow, be figured on 10,000 
feet velocity. 

Example. — Required the diameter of the main steam-pipe 
leading from a battery of boilers having an aggregate of 3000 
boiler horse-power. Assume the pressure to be 100 pounds 
by the gauge, or about 115 pounds absolute. Assume also that 
a boiler horse-power is equivalent to 30 pounds of steam per 
hour. Then the steam drawn from the boiler in one hour is 

30 X 3000 = 90,000 
pounds. The steam per minute is consequently 1500 pounds. 

Now one pound of steam at 115 pounds absolute has a 
volume of 3.862 cubic feet. Consequently 
1500 X 3.88 = 5820 
cubic feet of steam per minute must pass through the steam- 
main. With a velocity of 5000 feet per minute the area of the 
pipe must be 

5820 + 5000 = 1. 164 



STEAM-BOILERS. 379 

square feet, or 167.6 square inches. The corresponding diameter 
is 14^ inches. The next larger size of pipe is 16 inches, which 
will be used. 

In calculating the size of the steam-pipe needed for a battery 
of boilers the lowest pressure at which the boilers will ever work- 
must be considered, for a pipe which will carry 500 H.P. at 150 
pounds pressure will carry only about 3/4 of 500 at 100 pounds 
pressure with the same velocity. 

Flow of Steam in Pipes. — Various formulae have been 
proposed for use in figuring the weight of steam a pipe will deliver 
with a cretain drop in pressure. 

An article by Prof. G. F. Gebhardt in Power, 1907, compares 
all of these formulae. 

It would seem that the formulae proposed by Mr. G. H. 
Babcock give results which agree very closely with results ob- 
tained by experiment. 
In this formula 

w = the weight of steam in pounds per minute; 
d = diameter of pipe in inches; 
L = length of pipe in feet ; 

P = the drop in pressure in pounds per square inch; 
;y = the mean density in pounds per cubic foot; 
V = velocity in feet per minute. 



^ = 15,950 



3.6\' 



K-¥) 




380 STEAM-BOILERS. 

Steam Meters. — There are a number of different kinds of 
steam meters in use to-day. The most common are the 
St. John, the Dodge or General Electric, and the Gebhardt. 
The last two consist of a Pitot tube used to measure velocity. 

The tube is the same in principle as that already explained 
in connection with the subject of induced draught-fans, but is 
made much stiffer and stronger. 

The greater the velocity of the steam in the pipe the more 
reliable are the readings. 

In the large boiler plants built recently, it has been the 
custom to connect a steam meter of the Pitot-tube type in the 
pipe leading from each boiler into the main. 

These meters tell at a glance what each boiler is doing, and 
have proven a great help to the men in charge of the different 
fire rooms. 

The meters are generally self-recording, and these, together 
with recording steam gauges, C0 2 recorders, high and low water 
alarm whistles, and recording volt-meters and ammeters, make 
it possible for an engineer to tell from his office the condition of 
his entire plant. 

Pipe-covering. — The steam-pipes should be covered with 
some non-conducting material to prevent radiation of heat. 
Magnesia, asbestos, mineral wool, hair-felt, etc., have been used 
for such coverings. 

Generally a sectional covering is used on the straight pipe and 
plastic on the fittings. 

It is probable that four tenths of a heat-unit will be lost per 
square foot of pipe surface per hour per degree difference of 
temperature between the steam inside the pipe and the air, if any 
good covering from 1 inch to i\ inches in thickness is used. A 
bare pipe would lose from 2.5 to 3 heat-units in radiation from 
each square foot per hour and per degree difference of temper- 
ature. The saving to be made by covering the pipes is apparent. 

Tube-cleaners. — To remove the scale which collects on the 
inside of the tubes of water-tube boilers supplied with a poor 
grade of feed-water, turbine tube-cleaners are used. 



BOILER ACCESSORIES. 



381 



Figs. 173 and 174 show the Liberty tube-cleaners. The head 
shown by Fig. 173 is for hard scale and also for use in a bent 
tube. 




\a 



p 



Fig. 173. 

Fig. 174 shows a different head attached to the turbine. The 
turbine blades are seen in Fig. 174. Water from a hose is taken 
into the outer casing. The water in escaping passes through 
the turbine, which rotates at high velocity, throwing out the 
arms with cutters by centrifugal force. The scale removed is 
washed away by the water. 




Fig. 174. 



The Weinland turbine cleaner is shown by Figs. 175 and 176. 
The lower right-hand figure is in section. The porcupine head, 
which is used on heavy scale, is shown at the left. 

This, like the preceding, operates with a i^-inch hose. 

A cleaner for removing soot from the inside of fire-tubes is 
shown by Fig. 177. This is attached to a long rod and pushed 
through the tube. 



3 82 



STEAM-BOILERS. 




Fig. 175. 




Fig. 176. 




Fig. 177. 



CHAPTER X. 

COAL HANDLING AND COAL-HANDLING MACHINERY. 

Coal-conveying Apparatus. — Until recently but little of 
value has been written on the subject of conveyors. An article 
by Mr. W. G. Hudson in the Engineering Magazine, vol. 37, 
1909, and articles by Messrs. G. E. Titcomb, S. B. Peck, and 
C. K. Baldwin, in 1908 Transactions of A.S.M.E., cover the 
subject quite fully. Much of what follows has been abstracted 
from these articles. 

Conveyors for the continuous nandling of coal or other 
material may be divided into two general classes : 

(a) Those which push or pull their load, the weight of the 
load not being borne by the moving parts of the conveyor. 

(b) Those which actually carry the material handled. 
Conveyors of the first class push or pull the material 

handled in a trough. The friction of the conveyor itself and 
of the material conveyed on the trough both consume power 
and cause wear. Hence the field of usefulness of conveyors 
of this type is confined to relatively small conveyors with 
light service; or in the larger installations, to the handling of 
materials with a low coefficient of friction, and which are not 
abrasive in their action, such as coal, grain, etc. 

Flight Conveyors. — One of the oldest forms which, from its 
simplicity and comparatively low first cost, is still one of the 
most extensively used, consists merely of an endless chain to 
which are attached, at intervals, scrapers or flights. The im- 
proved forms of this conveyor, now most generally used, have 
sliding shoes or rollers attached to the flights or the chains, 
supported on runways. The flights are allowed to come very 
close to the trough bottom, but not actually in contact with it, 

383 



384 



STEAM-BOILERS. 



thus reducing the friction upon the trough to the minimum 
amount. 

The accompanying figure (Fig. 178) illustrates a single-strand 
flight conveyor. 




Fig. 178. 

CONVEYING CAPACITIES OF FLIGHT CONVEYORS. 

S. R. Peck, A.S.M.E., 1910. 

In tons (2000 pounds) of coal per hour at 100 feet per minute. 





Horizontal. 


Inclined. 


Size of 
Flight. 


Spaced. 


Pounds per 
Flight. 


IO°. 

24 Inches. 


20 °. 
24 Inches. 


*>•. 




18 Inches. 


18 Inches. 


24 Inches. 


24 
Inches. 


4X10 
4X12 
5Xl2 

5X15 
6X18 


33f 
42! 

69I 


30 
38 
46 
62 
80 
120 


22^ 

28! 

345 

46^ 

60 

90 

105 

135, 

1725 


15 
19 
23 
31 
40 
60 
70 
90 
115 


18 

24 ■ 
28! 
4o| 
492 
72 
84 
120 

150 


I4l 

18 

22i 

312- 
4o£ 
57 
66£ 
96 
120 


10? 

I3f 

i6£ 

22^ 

31* 

48 
56 
72 
90 


8X18 




8X20 




8X24 
10X24 















The horse-power required for handling anthracite coal may 
be determined from the following formula, this taking no account 
of gearing or other driving connections. 

A TL + BWS 



H.P. = 



1000 



COAL HANDLING AND COAL-HANDLING MACHINERY. 385 

T = net tons per hour. 
L = length, centre to centre, in feet. 
W = weight of chain and flights (both runs) in pounds. 
S = speed per minute in feet. 

A and B are constants depending on the inclination from the 
horizontal. (See values below.) 

TT OOOOO O O O O 

Hor. 5 10 15 20 25 30 35 40 45 
A 0.343 0.42 0.50 0.585 0.66 0.73 0.79 0.85 0.90 0.945 
B 0.01 0.01 0.01 0.01 0.009 0.009 o-OOQ. 0.008 0.008 0.007 

The common working speeds are from 100 to 200 feet per 
minute, and the capacities are as shown by the table, these con- 
veyors in some cases handling upwards of 500 tons per hour. 

As an illustration, suppose it is desired to elevate hard coal 
50 feet by a flight conveyor inclined 30 degrees, the capacity 
of the conveyor being 30 tons per hour at 100 feet speed per 
minute. From the table it is evident that at a speed of 100 
feet per minute the flight should be 6 inches by 18 inches and 
spaced 24 inches apart. 

The length of the conveyor, centre to centre, would be at 
least 100 feet. 

Calling the weight of the chain 20 pounds per foot, and the 
weight of the flights spaced every 2 feet, 40 pounds, as given, the 
total weight per foot figures as 40 pounds. 

Substituting, in the formula given, the 

_ 0.79 X 30 X 100 + 0.009 X 200 X 40 X 100 

1000 
= 7-77- 
Pivoted-bucket Carriers. — Where the design of the plant re- 
quires conveying machinery adapted to the combined service 
of handling coal and ashes, the pivot-bucket carrier is hard to 
excel. The handling of ashes is very hard on conveying ma- 
chinery, and the construction of the carrier permits replacement 
of the several parts as corrosion or wear proceeds. 



386 STEAM-BOILERS. 

Typical of this combined service is the recent installation in 
the new Wanamaker power house in Philadelphia. Here the 
inaccessible position of the storage bunkers makes it imperative 
that the conveying machinery should be reliable. Coal is de- 
livered by wagons at the street level to a reciprocating feeder, 
and is carried by a Dodge carrier up and over the storage bins. 
The lower horizontal run of the machine brings it beneath the 
ash discharge gates, so that ashes may be handled between the 
intervals of coaling. Steam sizes of anthracite coal are burned 
exclusively. 

This carrier operates at a speed of 42 feet per minute. The 
vertical lift is 114 feet. Power required when operating un- 
loaded, 6 horse-power; loaded, at 40 tons per hour, 16 horse- 
power, showing good efficiency. 

The buckets are of malleable iron, about 1/4 inch thick and 
24 by 24 inches in plan. The ends of the shafts carrying the 
buckets form the chain pins. The inner links are bushed to 
obtain the necessary bearing surface, oil ducts extending into 
the bearings from the ends of the shafts. The bushings are 
protected by chilled cast-iron collars which engage the driving 
sprockets. The flanged self -oiling rollers, spaced midway in the 
links, support the carrier on the horizontal runs and do not 
engage the sprockets. 

Pivoted-bucket carriers for elevating coal in power-plant 
service have become quite popular. Their advantages are slow 
speed, silent operation, adaptability to change of direction with- 
out transfer, high efficiency, and easy renewal of worn parts. 
Their disadvantages are danger of buckets sticking or upsetting 
and jamming in the supports, and the difficulty of preventing 
spill at the loading and turning points. Protection against 
jamming may be had by connecting with the driving machinery 
through a safety pin whose margin of strength beyond the 
power requirements is very slight; or better, by designing the 
supports so that the buckets will clear in whatever position they 
may come around. 



COAL HANDLING AND COAL-HANDLING MACHINERY. 387 

Uncleanly loading is guarded against in various ways in the 
several latest designs of carriers, of which the following may be 
noted. 

In the Hunt carrier, Fig. 179, the buckets are spaced an inch 




Fig. 179. 

or so apart and are loaded by a special device consisting of a 
series of connected funnels at the loading chute, Fig. 180, in 




Fig. 180. 

synchronism with, and dipping into, the carrier buckets, so that 
each bucket received its proper charge only. 

The Webster carrier has buckets with carefully planed lips, 
and the pitch of the buckets being very slightly less than the 
pitch of the carrier chain links, thus depending on close contact 
to eliminate the leakage. 

The McCaslin carrier, made now by the Mead, Morrison 



3 88 



STEAM-BOILERS. 



Manufacturing Company, uses overlapping buckets. These lap 
the wrong way after tripping for discharge, and are reversed 
by a " righting mechanism " before again passing the loading 
point. 

The Dodge carrier, Fig. 181, uses small auxiliary buckets 
hung beneath the apertures between the main buckets to catch 
the drip and return it to the main buckets at the first upturn. 







Fig. 181. 

The auxiliary buckets are shown fastened rigidly to the 
inner links. These auxiliary buckets are horizontal and at 
right angles to the chain on vertical lifts. 

Fastened to the end of the main carriers or buckets there is 
a cam which serves to dump the bucket, the arrangement being 
similar to that shown by the next illustration. 

The Peck carrier, Fig. 184, uses overlapping buckets similar 
to the McCaslin, but they are attached to the links extended 
beyond the points of articulation. This arrangement unlatches 
the buckets at the turns by giving them a path of greater radius 
than the chain joints, thereby doing away with a righting device 
otherwise necessary with the overlapping bucket. 

None of these devices for preventing spill at the loading and 



COAL HANDLING AND COAL-HANDLING MACHINERY. 389 

turning points are particularly effective. The difficulty is in- 
herent in this type of conveyor whose many advantages, how- 
ever, far outweigh their defects. 

The alternative of the pivoted-bucket carrier for handling 
coal is the standard arrangement of an elevator with rigid steel 
buckets discharging into a flight conveyor which crosses above 
the bunkers, and is provided with discharge gates at convenient 
intervals; or instead of a flight conveyor, a belt with movable 
tripper, Figs. 182 and 183. This is a well tried-out system, 




o^R 



Fig. 182. 




Fig. 183. 

thoroughly reliable, and by many preferred to the run-around 
carrier on the ground, of lower first cost and simpler construc- 
tion. The elevator conveyor system is not adapted to handling 
ashes, which, however, should be taken care of by separate 
machinery whenever possible to do so. 

Screw conveyors for boiler-house service are sometimes used 
where the capacities are not large. In their favor it may be said 
that they are compact and lowest in first cost. Against them 
are the objections negligible in small installations, but increas- 



390 STEAM-BOILERS. 

ingly undesirable in larger ones, that they are wasteful of power, 
unreliable if handling bituminous coal, and of high maintenance 
cost. 

The general arrangement of a " rectangular " pivoted bucket 
conveyor is shown by Fig. 184. 

Coal discharged from a car or from a cart falls into a hopper, 
from which it is fed by a reciprocating feeder into a crusher 
where the large lumps are broken up. From the crusher the 
coal is taken directly into the conveyor or into the feeding 
mechanism which fills the conveyor. 

» Somewhere in the system there must be a tightener, which 
in this cut is shown as located at the lower right-hand corner. 

The reciprocating feeder consists simply of a movable plate, 
at the bottom of the hopper, which is pushed forward and back 
through the action of an eccentric. On the forward stroke coal 
is fed into the crusher. The length of the plate is such that 
coal in the hopper will not flow over the left-hand edge when the 
feeding plate is still. 

Maryland Steel Company's Coal-handling Equipment. — An 
interesting example of coal handling in large capacities is ex- 
hibited by the equipment of the Otto coke plant of the Mary- 
land Steel Company, which has been very successful in its 
operation. 

Coal is delivered from four track hoppers, equipped with 
automatic feeders, to two double-strand monobar scraper lines 
117 feet centres, with suspended flights every 3 feet. These 
conveyors deliver the coal to two crushers, and the product is 
elevated by two gravity discharge elevators, with 24- by 42-inch 
buckets spaced 3 feet apart. These discharge upon a 30-inch 
belt conveyor running horizontally 253 feet to the storage bins. 

The capacity of this installation, with all the machinery in 
operation, is 220 tons per hour, or, holding one elevator, crusher, 
and feeding conveyor in reserve, no tons per hour. 

The total cost of repairs in material and labor averages 
four tenths to five tenths of a cent per ton handled, and the 



39 2 



STEAM-BOILERS. 



labor cost of operating, about nine tenths of a cent per ton. 
The installation has been handled with intelligence and care, and 
to this, without doubt, much of the credit for its excellent record 
is due. Power readings at the motor are as follows: 



Machine. 



Each feeding conveyor 117 feet cen- 
tres: 30 feet rise, 10 by 42 inch 
suspended flights spaced 3 feet; 
speed 105 feet per minute 

Each pair of automatic feeders: 
Each plate 3 feet 6 inches wide 
by 11 feet long, stroke 6 inches. . . 



Each crusher: Two rolls 47 inches 
diameter by 36 inches long 



Each elevator: 94 feet vertical lift, 
16 feet horizontal run, V-buckets 
24 by 42 inches spaced 3 feet 
apart; speed 105 feet per minute. . 

Belt conveyor 253 feet centres ^cl- 
inch belt; speed 650 feet per min- 
ute. Moving tripper with belt 
empty runs up power of belt con- 
veyors to 14 horse-power. 



Size of 
Motor. 


Starting 
Load. 


Power 
Empty. 


H.P. 


H.P. 


H.P. 


25 


20 


5-8 


5 


5 


3 


50 


43 


8 


40 


27 


8 



Running 
Load. 



H.P. 



52 



12-17 



When the test was made, coal was being handled at the rate 
of 215 tons per hour, i.e., 107 J tons to each feeding conveyor, 
crusher, and elevator, and 215 tons per hour upon the belt. 
The life of a belt handling crushed coal is 18 months. The 
1/4-inch steel troughs for the monobar conveyors are good for 
about 20 or 22 months. An occasional flight must be replaced. 
The knuckles of the chain are of very ample wearing surface 
and of long life. The elevator is of unusually heavy construc- 
tion, with hardened chain pins and chilled driving rollers. The 
rate of wear here is very slight except at the pinions of the 
motor and countershaft. The brunt of the work comes upon 
the crushers whose business it is to reduce run-of-mine bitumi- 
nous to 1 inch and under. 



COAL HANDLING AND COAL-HANDLING MACHINERY. 393 

Power Required to Drive a Bucket Conveyor. — The power 
required to drive a bucket conveyor is rather difficult to figure, 
inasmuch as the same conveyor at different times requires dif- 
ferent amounts of power for the same work. From what data 
the authors have been able to secure through actual tests, it 
seems that for a bucket conveyor making a rectangular circuit 
with lift of from 40 to 80 feet of from 20 to 50 tons capacity, 
and at a speed of from 40 to 55 feet per minute, the horse- 
power required may be calculated by multiplying the capacity 
in tons per hour by the lift in feet and by 0.004. 

The conveyor when running empty will require from 40 to 
60 per cent of the power running loaded. The smaller the 
capacity, the larger the percentage of power empty to power 
loaded. 

The crusher through which the coal passes before going to 
the conveyor often requires as much power as the conveyor. 

Cost of Handling Coal. — The cost of labor for handling coal 
(not including interest and depreciation) is given by Peck in 
Trans. A.S.M.E., 1910, as if cents per ton, this being an aver- 
age value obtained from a number of large plants handling from 
1000 to 9000 tons per month. The coal was received in 50-ton 
self-cleaning cars and dumped into the hoppers leading to the 
conveyor. In some few instances the coal had to be shoveled 
out of the cars. The cost for such conditions ran up to 2 cents 
or over per ton. 

Gebhardt in " Steam Power Plant Engineering " says that 
" an average figure for handling coal by barrow is 1.6 cents per 
ton per yard, up to a distance of 5 yards, then about 0.1 cent 
per ton per yard for each additional yard. 

"With automatic conveyors the operating cost, not including 
the wages of firemen and water tenders, varies with the size of 
plant and the type of conveyor, and ranges anywhere from a 
fraction of a cent per ton to 4 or 5 cents per ton. The larger the 
plant and the greater the amount of coal burned, the lower will 
be the cost per ton. In comparing the relative costs of manual 



394 STEAM-BOILERS. 

and automatic handling, fixed charges of at least 15 per cent of 
the first cost of the mechanical equipment should be charged 
against the latter, in addition to the cost of operation. 

" In large central stations equipped with stokers and con- 
veyors and consuming 200 tons or more of coal in 24 hours, the 
cost of handling the coal from coal car to ash car, including 
wages of fireman and water tenders, will range between 10 cents 
and 18 cents per ton." 

Belt Conveyors. — The earliest conveying belts were perfectly 
flat, being supported by plain cylindrical rollers such as are still 
used for the returning run. In order to increase the conveying 
capacity without the material spilling off the edges of the belt, 
the rollers were somewhat dished, or made concave in form, 
causing the belt to assume the form of a shallow trough. In 
theory this is open to the criticism, that but one diameter of the 
concave roller can travel at the speed of the belt, and some 
slipping must therefore take place at every other diameter of 
the periphery. Careful observations have shown, however, that 
the belts invariably fail in other ways before any injury from 
this slipping becomes apparent. 

Before this fact was demonstrated, however, a supporting 
device, consisting of three independent rollers, the middle one 
horizontal, and the side rollers inclined some 35 or 40 , came into 
very general use, this arrangement giving the belt the form of a 
deep trough and adding greatly to its carrying capacity. 

Further modification of this was the substitution of two in- 
clined centre idlers for the one horizontal idler. This, while 
giving a relatively deep trough, overcame the sharp bends in 
the belt incident to the three-roll support and permitted the 
belt to assume a uniform curve. For belts of large capacity, 
the four-roll idler may, therefore, be considered the best modern 
practice. For smaller belts and moderate capacities, there is 
nothing better than the old concave roller referred to, which 
troughs the belt but slightly, and, therefore, insures the greatest 
durability. 



COAL HANDLING AND COAL-HANDLING MACHINERY. 395 

The conveying belts themselves are of cotton duck, woven 
solid; or of a number of plies varying from three to eight, stitched 
or cemented together with a composition of rubber and known 
as rubber belts. Canvas belts are plain duck, or are treated 
with some preservatives and painted with some compound. 
For many kinds of service they meet every requirement. For 
severe duty, where the cotton fabric, which is the strength of 
the belt, must be protected as perfectly as possible from dust, 
moisture, and cutting or wearing action, the rubber belts are 
preferable, and are usually made with a cushion of from 1/10 
inch to 1/4 inch, more or less, pure rubber on the carrying side, 
which protects the fabric until this cushion is worn away. 
Special types of belts have been extensively used, some having 
fewer plies of canvas and a heavier cushion of rubber in the 
centre where the belt is designed to receive and carry its heaviest 
load, and others having the fabric made thinner at the points 
where it is intended the belt should be bent to form a trough. 
Experience seems to show that the greatest durability is at- 
tained by avoiding a localized bending. 

The belt conveyor has a wide field of usefulness and is 
deservedly popular both with manufacturer and user. It is 
simple, smooth, and noiseless in operation, and may be run at 
relatively high speeds, from 300 to 800 feet per minute, with con- 
sequent large conveying capacity. On account of the expense 
of the belt, and the large number of supporting rollers which 
revolve at high speed, the initial cost and the power consumed 
in operation are much greater than would be supposed, and not 
materially less than heavier and more cumbrous looking con- 
veyors of other types, performing equivalent service. 

The most serious objection to belt conveyors, and the one 
which has prevented their even more general use, is the lack of 
durability of the belts, their liability to destruction from acci- 
dental causes, and the expense of their frequent renewal. 

Capacity of Belt Conveyors. — Belt conveyors may be built to 
handle practically any quantity of material which may be fed 



396 



STEAM-BOILERS. 



to them. The following table gives the capacity, maximum size 
of lumps, and advisable speed for the different widths of belts. 

BELT CAPACITY AND SPEED. 



Width of 
Belt. 


Maximum Size 
of Pieces. 


Maximum Advis- 
able Speed in Feet 
per Minute. 


Capacity in Cubic 
Feet at the Maxi- 
mum Advisable 
Belt Speed. 


12 


2 


300 


1,380 


14 


25 


300 


1,890 


16 


3 


300 


2,460 


l8 


4 


350 


3.640 


20 


5 


350 


4,480 


22 


6 


400 


6,200 


24 


8 


400 


7,400 


26 


9 


450 


9,810 


28 


12 


450 


11,250 


30 


14 


450 


I3.050 


32 


15 


500 


16,500 


34 


16 


500 


18,500 


36 


18 


500 


21,000 


38 


19 


550 


25.300 


40 


20 


550 


28,050 


42 


20 


550 


30,800 


44 


22 


600 


37,200 


46 


22 


600 


40,800 


48 


24 


600 


44,400 



Speed and Size of Belts. — When the quantity to be con- 
veyed is small, and the pieces large, the size of the material 
fixes the width of the belt, and the speed should be as low as 
possible to carry safely the desired load. 

When the quantity is great, the capacity fixes the width, and 
in this case also the speed should be as low as possible. A 
belt at slow speed may be loaded more deeply than one at high 
speed, and when a narrow belt is run much above the advisable 
speed, the load thins out and the capacity does not increase as 
the speed. 

The maximum length of the different widths of conveyors is 
determined by the fibre stress in the belt, and is, therefore, 
closely related to the load and speed. Naturally level conveyors 



COAL HANDLING AND COAL-HANDLING MACHINERY. 397 

may be built longer than those lifting material. Conveyors 
1000 feet from centre to centre, handling 400 tons per hour, have 
been most satisfactorily operated. 

Another important factor in the design of conveyors at high 
speed handling large quantities is the flow of material in the 
chutes. A 36-inch conveyor handling 750 tons of coal per hour, 
with a belt speed of 750 feet per minute under a 10,000-ton 
pocket, could not be loaded from a single chute, because it was 
not possible for the coal to attain a speed of 750 feet per minute 
in the chute. It was necessary, therefore, in order to obtain a 
full load, to open seven gates, each placing a layer of coal on the 
belt until the desired load was obtained. During a test this 
belt carried about 800 tons per hour. 

Power Required for Belt Conveyors. — The power required to 
drive a belt conveyor depends on a great variety of conditions, 
such as the spacing of idlers, type of drive, thickness of belt, etc. 
In figuring the power required, it is important to remember 
that the belt should be run no faster than is required to carry 
the desired load. If for any reason it is necessary to increase 
the speed, the figure taken for load should be increased in pro- 
portion and the power figured accordingly. In other words, 
the power should always be figured for the full capacity at the 
chosen speed, as follows: 

C = power constant from table, page 398; 

T = load in tons per hour; 

L = length of conveyor between centres in feet; 

H = vertical height in feet that material is lifted; 

S = belt speed in feet per minute; 

B = width of belt in inches. 

For level conveyors, 

Hp _ CX TXL 
1000 
For inclined conveyors, 

Hp _ CXTXL TXH 
1000 1000 



398 



STEAM-BOILERS. 



Add for each movable or fixed tripper horse-power in col- 
umn 3 of table below. 

Add 20 per cent to horse-power for each conveyor under 
50 feet in length. 

Add 10 per cent to horse-power for each conveyor between 
50 feet and 100 feet in length. 

The above figures do not include gear friction, should the 
conveyor be driven by gears. 



POWER REQUIRED FOR GIVEN LOAD. 





1 


2 


3 


4 


5 


Width of 


C 


C 


H.P. 






Belt. 


For Material For I 


Material 


Required for 


Minimum 


Maximum 




Weighing from 25 Weighii 


lg from 75 


Each Movable 


Plies of 


Plies of 




Lbs. to 75 Lbs. per Lbs. tc 


) 125 Lbs. 


or Fixed Trip- 


Belt. 


Belt. 




Cu. Ft. per ( 


: u . Ft. 


per. 






12 


•234 


147 


1 


3 


4 


14 




220 


143 


1 


3 


4 


16 




220 


140 


3 
4 


4 


5 


18 




209 


138 


I 


4 


S 


20 




305 


136 


ll 


4 


6 


22 




199 


133 


I§ 


5 


6 


24 




195 


131 


if 


5 


7 


26 




187 


127 


2 


5 


7 


28 




175 


121 


2\ 


5 


8 


30 




167 


117 


2| 


6 


8 


32 




163 


115 


2| 


6 


9 


34 




161 


114 


3 


6 


10 


36 




157 


112 


si 


6 


10 



With the load and size of material known, choose from the 
capacity table the proper width of belt and proper speed. The 
above formulae give the horse-power required for the conveyor 
when handling the given load at the proper speed. With the 
horse-power and the speed known, the stress in the belt should 
be figured by the following formula in order to find the proper 
number of plies. 

Stress in belt in pounds per inch of width = ' — ^5j 

^ S X B 

With this value known, the number of plies may be determined, 



COAL HANDLING AND COAL-HANDLING MACHINERY. 399 

using 20 pounds per inch per ply as the maximum. Columns 
4 and 5 of this table give the maximum and minimum advisable 
plies of the different widths of belt. Belts between these limits 
will trough properly and will be stiff enough to support the load. 
The maximum number of plies determines the maximum length 
of each width of conveyor. 

Belt conveyors may be driven from either end. Somewhere 
in the system there must be a tightener to allow for the stretch 
of the belt. The troughing idlers should be placed dependent 
upon the weight of material carried as follows: 

For belts 12 to 16 inches wide, from 4J to 5 feet apart. 
For belts 18 to 22 inches wide, from 4 to 4 J feet apart. 
For belts 24 to 30 inches wide, from 3^ to 4 feet apart, and 
For belts 30 to 36 inches wide, from 3 to 3! feet apart. 

The life of the belt depends a great deal upon the care which 
it receives, upon the material handled, and upon the quality of 
the belt to begin with. In general the life of the belt may be 
taken as from three to eight years. 

The Darley Conveyor. — A system for handling coal or ash 
by a current of air flowing in a pipe has been in use in some 
plants during the last three years. A description of a system 
arranged for handling ash will show the method of operation. 
A pipe is laid under the floor in front of the boilers with an open- 
ing through the floor into the pipe in front of each ash-pit door, 
each opening being closed unless ash is being hauled from the 
ash-pit into it. The end of the pipe under the floor is open to 
the air. The other end of this pipe connects with a riser which 
leads up to the top of a closed steel storage tank in which the 
ash is to be stored. An exhaust fan or a Root exhauster draws 
air out of the tank, thus creating a flow in the pipe in front 
of the boilers. Any ashes, clinker, or even bricks dumped in 
through the holes in front of the boilers will be carried along by 
the air and delivered into the closed tank elevated 20 to 40 feet 
above the boilers. After the exhauster has been stopped the 



400 



STEAM-BOILERS. 



ashes may be discharged from this tank into a car or cart by 
opening an ash valve in the bottom. 

To quench the hot ash and to prevent dust from being drawn 
over into the exhauster, a jet of water is sent in on the ash as 
it is entering the closed tank. 

The fittings, especially those at the corners where the direc- 
tion changes, wear rapidly. The elbows are made with renew- 
able chilled backs or in some cases a tee is used in place of an 
elbow. The plugged end of the tee filling up with ash causes 
the wear to come on the ash. 

Coal Crushers. — The construction of a coal crusher is shown 
by Fig. 185. The casing is removed so as to show the rolls. 




The front roll can move back with its bearings compressing 
the springs when a railroad spike or a coupling pin jams in be- 
tween the rolls. To allow for such motion the teeth of the driv- 
ing gears are made of the involute type and are of extreme 
length. 

Rolls 17 inches diameter by 24 inches long will reduce run- 
of-mine bituminous with lumps not exceeding 10 inches by 10 
inches to 2\ inches size or less, at the rate of 30 tons per hour; 
and will require about 5 horse-power. 

Rolls 28 inches diameter 24 inches long will handle about 
50 tons per hour and consume about 10 horse-power. 

Rolls 28 inches diameter 36 inches long will handle 70 tons 
per hour and require 15 horse-power. 



COAL HANDLING AND COAL-HANDLING MACHINERY. 401 

Coal Valves. — Figs. 186 to 190 illustrate some of the types 
of valve used. 

General Arrangement for Handling and for Storing Coal in 
the Boiler House. — Figs. 191 and 192 illustrate two different 
equipments. The cuts need little explanation. 

A coal supply sufficient for from four to fourteen days may 
be stored in the coal bins overhead. 

From these bins or pockets the coax is fed by gravity to the 
mechanical stokers. The amount of coal used is weighed on 
its way from the pocket to the stoker by some form of weighing 
hopper, which may or may not be automatic; in general, similar 
to those shown by Figs. 195 and 196, and arranged as shown in 
Fig. 192. 

The ash may be taken into ash cars, as shown in Fig. 192, 
or be taken into cars which are later dumped into a hopper, 
from which a bucket conveyor elevates the ash to a storage 
hopper. Such an arrangement is shown in Fig. 191, in which 
the ash conveyor runs up in a vertical shaft, side of the coal 
conveyor, and turns to the right, where it, together with its driv- 
ing mechanism, may be seen in the landing over the large hopper 
into which the ashes are ultimately dumped. 

The storage bin is commonly designed as in Fig. 191, re- 
cently, however, a form of bin known as the parabolic bin has 
found favor among engineers. 

Such a bin is easy to calculate and brings but little side stress 
on the columns. The true shape of the curve would be found 
to be somewhere between a parabola and a transformed catenary. 

The parabola may be constructed as in Fig. 193 and its 
area figured as 2/3 xy, Fig. 194. 

The Brown Hoisting Machinery Company construct a bin of 
this type as follows: Two parallel plate girders are supported 
by the steel columns at the top of the pocket. From these 
girders, at intervals of 3 feet to 4 feet 10 inches, are suspended 
a series of steel supporting straps each curved approximately to 
the shape of a parabola. The straps are made strong enough to 




Fig. i 88. 




Fig. 189. 




Fig. 190. 



(402) 



404 



STEAM-BOILERS. 




Fig. 192. 



COAL HANDLING AND COAL-HANDLING MACHINERY. 405 



carry the weight of the lining of the bin and the coal which the 
bin is intended to hold. The bin is lined with " ferro-inclave " 
reinforced concrete from 2 inches to 4 inches thick on the inside, 
and later similarly coated on the outside. 



\ 


i 


i 




1 




Fig. 194. 



Fig. 193. 

The reinforcing steel is of peculiar shape, well adapted to 
this kind of construction. 

Weighing Hoppers. — Two makes of travelling weighing 
hopper are shown — that made by the C. W. Hunt Company, 
by Fig. 195, and that by the Link Belt Company, by Fig. 196. 

The weighing system of Fig. 196 consists of two shafts or 
rods, one of which is shown as AAB in the left-hand view, to 
each of which is attached two short cranks A A, which act as 
levers. 

By referring to the right-hand view it will be noticed that 
the outer ends of these cranks are hung by links and knife edges 
from the moving framework above. 

The hopper is carried by two bars which are hung from knife 
edges on these four levers in such a way that as coal comes into 
the hopper it tends to cause the inner ends of these levers to 
lift. 

Fastened to each shaft or rod there is at one end of each a 
lever B, and these two levers pull up on a common rod which is 
connected with the weighing lever at the bottom. 



406 



STEAM-BOILERS. 




COAL HANDLING AND COAL-HANDLING MACHINERY. 407 




Fig. 196. 



CHAPTER XI. 
SHOP-PRACTICE. 

The method of work in a boiler-shop depends on the size 
and arrangement of the shop and on the class of work. 
There are, however, certain general principles which can be 
recognized in all modern shops. 

The materials, especially the plates, are received at one 
end of the shop, near which is a storeroom, and a bench for 
laying out work. The plates, after they are laid out, pass in 
succession to the several machines, where they are sheared, 
punched or drilled, planed, rolled, and riveted. The machines 
for performing these operations are arranged in order with 
proper spaces for handling and working. Space is provided 
where boilers may be assembled and receive their tubes and 
furnaces. Machines which, like the punch, have much work 
to do, compared with other machines, may be duplicated. 

There should be an efficient system for handling the 
material at the machines and for passing it on from one 
machine to the next. A good arrangement is to have a 
swing-crane near each machine ; the spaces served by the 
several cranes overlap, so that one crane takes material from the 
next, and so on. It is advantageous, especially in large shops, 
to have a travelling crane that can handle the largest boiler 
made, and which can serve any part of the shop. 

Flanging and smithing are usually done in a separate shop 
or room. A few machine-tools are needed for doing work on 
steam-nozzles, manhole rings and covers, etc. 

A boiler-shop will have an office, a drawing-room, and a 

408 



SHOP-PR A C PICE. 4 00 

pattern-room, also a storeroom for patterns. These may be 
conveniently located in the second story. 

A Boiler-shop. — The application of the general princi- 
ples just stated and the explanation of details can be best 
given by aid of an example. A medium-size shop for making 
cylindrical boilers has been chosen for this purpose; the 
shop is capable of making any shell boiler of moderate size. 
This shop will employ sixty or seventy men and can turn out 
two ioo-horse-power boilers per day. It will take about 
three days to finish one boiler, so that there may be six or 
more boilers in process of construction at one time. 

The shop which is represented by Fig. 197 has one end 
on the street and has a driveway or yard at one side. Plates 
are received at the street-door by a travelling crane and stored 
near at hand. The same crane takes plates to the laying-out 
bench and from there to the crane which serves the shearing- 
machine. Along one side of the shop are arranged in suc- 
cession a shearing-machine, two punches, a plate-planer, a 
*et of plate-rolls, and a riveting-machine. Between the 
punches and nearer the wall is a flange-punch ; near the 
planer is a forge for scarfing. This series of machines is 
served by four swing-cranes, and there are also two hydraulic 
cranes near the riveting-machine. These cranes, which are at 
the top of a tower thirty feet high, are operated from the 
working platform of the riveter. There are two shipping- 
doors where the finished boilers are delivered to teams, and at 
each door there is a jib-crane for handling the boilers. These 
jib-cranes and the hydraulic cranes at the riveter have a 
capacity of eight or ten tons; the swing-cranes may be much 
lighter. A shop where large marine boilers are made will 
have more powerful cranes. 

The machine-shop is near the receiving-door. Here are 
the lathes, planers, and drills for doing work on manholes, 
nozzles, and other fittings ; also a bench for fitting up boiler- 
fronts. Two drills for boring tube-holes in tube-plates, and 



4io 



S TEA M-B OILERS. 





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133H1S 



SHOP-PR A C TICE. 

411 

a boring-mill for facing off the flanges of boiler-heads, are 
placed in the entrance to the machine-shop, where work can 
be conveniently brought to them from the boiler-shop. At 
the end partition of the machine-shop are places for storing 
boiler-front castings and sheet-iron. The corner of the boiler- 
shop near the machine-shop is known as the cold-iron shop ; 
here the uptakes, flues, and dampers are made. This shop 
has a shearing-machine, three punches, and a set of rolls 
suitable for sheet-iron work; also a bench with hand-vises. 

At the rear of the boiler-shop there is in one corner a store- 
room for tubes, stay-rods, channel-bars, and finished fittings. 
In the opposite corner are the forge-shop and the engine- 
room. These are separated from each other and from the 
boiler-shop by glass partitions which do not cut off the light, 
and yet keep the smoke and dust from the forge out of the 
other rooms. 

The main line of shafting is near the wall over the shear- 
ing-machine, punches, and rolls. The shafting for the ma- 
chine-shop and cold-iron shop is driven by a belt from the 
main shaft, near the front end of the building. A space is 
left near the riveter where the plates from the rolls can be 
assembled and bolted together before going to the riveter. 
In front of the riveter there is a space about 60 feet wide 
and 120 feet long where boilers are deposited after leaving 
the riveter. Here the boilers receive their stays and tubes, 
here they are calked and receive all fixtures that are perma- 
nently attached to the shell. At this place the boilers are 
tested by hydraulic pressure, usually to one and a half times 
the working pressure. When complete the boilers are painted 
and oiled, ready for shipment. 

To illustrate the method of building a boiler more in 
detail, the different steps in making a horizontal boiler will 
be followed in order. 

Flanging Heads. — Regular sizes of boiler-heads flanged 
at one operation by machinery can now be bought on the 



4 12 STEAM-BOILERS. 

market, and all except the largest shops are in the habit of 
buying them. The flanging-machine has a former and a die 
between which the plate is formed under hydraulic pressure 
while at the proper flanging temperature. No strains due to 
unequal heating or cooling are set up in this process, and 
the plate, which is allowed to cool gradually, does not need 
to be annealed. 

Irregular sizes and shapes are made in the shop on a 
special cast-iron anvil, which is about six inches deep, flat on 
top, and curved at one side to about the radius of the head to 
be flanged. The corner of the anvil or former is rounded so 
as not to cut the plate. It is placed near a special low forge 
where the plate is heated. 

In flanging, the plate is first marked at short distances on 
the inner circle of the bend with a prick-punch. A portion 
of the plate is then heated to a good heat, and the plate is 
taken to the anvil or former. After adjusting so that the 
depth of flange overhangs the right distance from the edge 
of the former, the heated portion of the plate is beaten down 




Fig. 19S. — Lifting-dogs. 

against the side of the former by wooden mauls and then 
smoothed with a flatter and sledge. The plate is then heated 
in a new place and another portion bent. To straighten the 
head and also to remove the strains set up by this way of 
flanging, it should be heated to a dull red and allowed to cool 
gradually. 

The lifting-dogs represented by Fig. 198 are used in lift- 



SHOP-PRACTICE. 



413 



ing and placing the head during the flanging, and in handling 
plates during other operations. 

Fig. 199 represents crane-lifts which are used when plates 
are lifted and carried by cranes. 




Fig. igg. 

After the head is flanged, holes for rivets, stay-rivets, 
and tubes are marked, and all the rivet-holes are punched. 

Flange-punch. — The holes in the flange are punched by 
a special machine shown by Fig. 200. The punch is carried 




Fig. 200. 



by a horizontal wrought-iron plunger which is operated by a 
cam. The die is carried by a hooked extension of the frame. 
The head is held horizontal with the flange down ; the flange 
is dropped between the punch and the die and the lever is 



4 i4 



S TEA M-B OILERS. 



solid piece of tool-steel. 




pulled to throw the cam into play ; the plunger then makes 
a stroke and punches a hole. The machine is driven by a 
belt, with a fast-and-loose pulley. On the shaft with these 
pulleys is a heavy fly-wheel. A pinion and spur-gear give a 
slow powerful stroke to the gear which moves the cam. 

Punch and Holder. — The punch (Fig. 2 oi) is made of a 

It has a flat head and a conical 
shoulder by which it is held onto 
the plunger, a short straight body, 
and a slightly coned point. The 
point is larger at the cutting edge 
than back toward the straight 
body, to avoid friction in the hole. 
A tit in the middle of the face of 
the punch catches in the centre- 
punch mark and centres the hole punched. 

The holder is made of wrought iron. It screws onto the 
end of the plunger, grips the punch by the conical shoulder 
on its head, and draws it down firmly against the plunger. 
Tube-holes. — There are two ways of cutting the holes 
for the tubes in boiler-heads. Some- 
times a small hole is punched at the 
centre of the hole. A tool like that 
shown by Fig. 202 is then put in the 
drill-press. The post in the middle is 
run through the small hole previously 
punched or drilled, and the two cutters 
rapidly cut out the tube-hole to the 
proper size. 

The other way is to 
punch the tube-holes 
at once to the proper 
size by a helical punch 
shown by Fig. 203. The die is made in the form of a ring 
with a flat face, so that the punch begins to cut at the cor- 



rifl 




Fig. 202. 



Fig. 



203. 



SHOP-PR A CTICE. 4 1 5 

ners, and the metal is removed by a shearing cut. Though 
not always done, the holes ought to be punched a little under 
size and then reamed out to give a fair surface against which 
the tubes may be expanded. 

Finishing the Flange. — The boiler-heads are placed on 
the platen of a boring-mill like that shown by Fig. 204, and 
the edge of the flange is turned off. The heads of marine 
boilers are often turned to a true cylinder at the flange to insure 
that they shall exactly fit the cylindrical shell into which 
they are riveted. This also gives a good surface to calk 
against. 

Boring-mill. — A simpler machine than the boring-mill 
shown by Fig. 204 would answer to turn off the flanges of 
the boiler-heads. But the machine is useful in other ways 
and may do the work which is commonly done on a large 
lathe. 

The platen is driven much in the same manner as the 
head of a lathe, through gearing and cone pulleys, to provide 
for various speeds. This gearing is not well shown in the 
figure, as it is hidden by the frame. The cutting-tool is ad- 
justed and controlled much like the tool of a planer. The 
tool-carriage is on a horizontal cross-head which is supported 
at the side frame and on a round vertical bar at the middle. 
The tool can be traversed in and out on the cross-head, and 
the cross-head may be raised or lowered. 

For doing some classes of work the cross-head may be 
set vertically on the guides that are shown on the horizontal 
bars of the frame near the right-hand end. Or, again, a tool 
may be carried by the central rod, which can be fed down by 
the screw at the top. 

Laying on the Plates. — The first and one of the most 
important steps in the work on the shell is the marking out 
of the plates. Generally one man in each shop does all the 
laying out. After squaring the sheet, he marks off the 
length and locates the rivet-holes by means of gauges. These 



4i6 



S TEA M-B OILERS. 



gauges have to be made by trial, a suitable allowance being 
made in them on account of the thickness of the plate for the 




Fig. 204. 
change in length due to rolling. There is a gauge for each 
course, or a set of gauges for each size boiler, and also sets 



SHOP-PR A CTICE. 4 1 7 

for the same size, but with different thickness of shell. The 
plates are marked either with a piece of soapstone or with a 
slate-pencil. Rivet-holes are prick-punched at the centre. 
Shearing. — When the plate is laid out it is taken from 




Fig. 205. 

the bench to the shears and any superfluous stock is cut off. 
A shearing-machine is shown by Fig. 205. The lower knife 
is fixed and the upper knife is moved by an eccentric inside 
the head. The eccentric-shaft is coupled to the gear-shaft 
by a clutch that is controlled by a treadle. The weight of the 
sliding-head is counterbalanced by a weight and lever at the 
top. Lugs are shown on the casting near the knives ; when 
the machine is required to do extra-heavy work, wrought-iron 
bolts are put through the lugs and screwed up to strengthen 
the frame. 

The machine is driven by a belt with a fast-and-loose pul- 
ley ; the shaft carrying these pulleys has a pinion gearing into 
a large gear to give the necessary power for shearing. A fly- 
wheel steadies the motion of the machine; it must be able to 
supply the power for shearing-plates without a large reduction 
in speed. 



4i8 



S TEA M-B OILERS. 



Punch. — After the plate is sheared to size it is taken to 
one of the punches and all the rivet-holes are punched. Larger 
openings for man-holes and other fittings are cut out by punch- 
ing overlapping holes, thus leaving a ragged edge which is 
afterwards chipped smooth. The plate is not entirely cut away 
at such large openings, but the piece to be removed is left 
hanging at three or four places until after the plates are rolled 
into cylindrical form. If the pieces were removed, there would 
be less resistance to the rolls at such places and the plates 
would have a conical form instead of a true cylindrical form. 

The punches resemble the shears shown by Fig. 205, with 
a punch and die instead of the knives. Machines are often so 
made that they either punch or shear. 

Planing. — After the plate is sheared and punched the 
edges are planed to a slight angle to give a good calking 
edge. 

The planer shown by Fig. 206 has a long narrow bed on 
which the edge of the plate is laid and to which it is clamped 
by a follower; the follower is forced down by screws which 
pass through a beam as shown. The tool-carriage is drawn- 
back and forth by a leading-screw; the tool is made to cut on 
both strokes, and is fed by hand between the cuts. 

Scarfing. — When the plates are joined by a lap-joint the 
proper corners of each plate are heated in a portable forge 
near the planer, and are drawn down or scarfed so that the 
overlapping plates may come close together and not leave a 
space. 

Plate-rolls. — The plates for forming the cylindrical shell 
are bent to shape cold by running them through bending-rolls 
The horizontal roll represented by Fig. 207 has two parallel 
rolls below that are driven in the same direction by gearing. 
The upper roll is adjusted at each end separately, and some 
care is required or the shell will receive a conical shape instead 
of a true cylindrical shape. The bearing at one end of the 



SHOP-PRACTICE. 



419 




420 



STEAM-BOILERS, 




SHOP-PRACTICE. 



421 



roll can be swung out, as shown by the figure, to remove the 
plate after it is rolled. 

The rolls may be driven in either direction by crossed and 
open belts. The plate to be rolled has one edge introduced 




Fig. 208. 



between the upper and lower rolls, the upper roll is brought 
down and the rolls are started up. The plate is run through 
nearly to the other edge then the top roll is screwed down 



422 STEAM-BOILERS. 

farther and the rolls are reversed. Thus the plate is run back 
and forth and the top roll is gradually drawn down till the 
plate acquires the proper form. 

The extreme edges of the plate are not bent in this process; 
they are commonly bent afterwards by hammering them with 
sledges. Some rolls have a special device for bending the 
edges ; it consists of two short overhanging rolls about fifteen 
inches long, one concave and the other convex. The ends of 
the plate are fed through these rolls sideways, and are bent 
before they are introduced into the long rolls. 

Vertical rolls, shown by Fig. 208, are coming into use in 
boiler-shops. They take up less floor-space, and the plate after 
it is rolled up into cylindrical form is easily hoisted off from 
the front roll. For this purpose the front roll is counterbal- 
anced and the top end can be swung out clear from the hous- 
ing. The figure shows the rolls as erected by the builders; 
in the boiler-shop the plate at the lower end of the rolls is 
flush with the floor of the boiler-shop. 

The width of plate that can be rolled by either horizontal 
or vertical rolls depends on the length of the rolls. The 
length of the rolls and the reach of the riveter (to be men- 
tioned later) determine the width of plate that can be handled 
in the shop. 

Assembling and Riveting. — When the plates for a boiler 
have been punched, planed, and rolled they are assembled in 
courses, and bolted together ready for riveting. Formerly 
boilers were commonly punched and riveted ; now it is cus- 
tomary to punch the rivet-holes one eighth of an inch smaller 
than the finished size and then drill to the right size after the 
boiler is assembled. This is more expeditious than drilling 
directly, and as all the metal affected by punching is removed 
it gives as good results. It is the custom in most shops to 
drill the holes out at the riveting-machine immediately before 
the rivets are driven and thus each rivet-hole is sure to be 
true. 



SHOP-PRACTICE. 423 

The shells of heavy marine boilers are drilled after the 
plates are assembled without previous punching. A few holes 
are drilled before the plates are rolled and serve for bolting 
the plates in place when the boiler is assembled. There are 
two forms of machines for drilling marine-boiler shells. In one 
the boiler is placed horizontal on rollers so that it may be 
readily turned, There are two or three upright frames each 
carrying a drill. The frames may be adjusted lengthwise of 
the boiler, and the drills may be set at any height or turned at 
an angle. When a longitudinal seam is drilled the boiler is 
rotated to bring a row of rivets to a drill, and the frame is trav- 
ersed from hole to hole. When a ring-seam is drilled the 
drill is brought to the proper place, and the boiler is rotated so 
as to bring the rivet-holes in succession to the drill. The 
other machine has the boiler placed on one end and the verti- 
cal frames carrying the drills can be rotated into place, and the 
boiler can be turned on a vertical axis. 

If plates are punched and riveted without drilling, the 
holes should be punched from the side of the plate which 
comes in contact with the other plate. The reason for this 
is that the die is always a little larger than the punch and the 
hole is slightly conical, larger at the side where the die holds 
up the plate. If the smaller ends of the holes in two plates 
are brought together, then the rivet fills the hole better and 
draws the plates up more perfectly as the rivet cools. It is 
clear that three or more overlapping plates should always be 
drilled, as punched holes cannot always be brought together in 
a proper manner. This is aside from the desirability of drill- 
ing all rivet-holes. 

Returning now to the assembling of a cylindrical boiler, 
the process is as follows: The back head is put in the rear 
course or ring of the shell, and is bolted with six or eight bolts 
through the punched holes. The head and ring are hoisted 
up to the drill near the riveter, and six or eight holes are 
drilled at about equal distances around the seam holding the 



4 2 4 STEAM-BOILERS. 

head into the ring or course, and rivets are driven by the 
machine in these holes. The bolts are now taken from the 
punched holes, and all the remaining holes are drilled and 
riveted, completing the ring-seam through the flange of the 
back head. The reason for driving a few rivets first, at equal 
intervals, is that the errors of spacing, when any exist, are 
distributed, and are removed during the subsequent drilling; 
while such errors might accumulate and give trouble if the 
seam were riveted in succession beginning at one point, 
without first driving a few rivets at intervals. 

After the ring-seam through the flange of the head is 
completed, the longitudinal seam or seams are drilled and 
riveted. Here again a few rivets are driven at intervals 
before the seam is riveted up. A few holes at the ends of 
the seams are left for convenience in joining onto the next 
course. 

The head and first course are now lowered onto the next 
course, which has been assembled in readiness. A few bolts 
are put through the punched holes, and the two courses are 
hoisted up, drilled and riveted in the way already described 
for the rear course. 

When all the courses are riveted together the front head 
is put in with the flange out so that the rivets in that flange 
can be driven on the machine. The closing seams on a boiler 
which, like the Scotch boiler, has both heads set with the 
flange in, must be riveted by hand. 

Rivets are heated in a small forge near the riveter and 
are passed to a man inside the boiler, who picks them up in 
tongs, thrusts them through the holes from within and guides 
the head of a rivet up to the die which is inside the boiler. 
Sometimes the rivets are thrust through from without, in 
which case the man inside the boiler guides the point to the 
die. On the platform of the machine stand the riveter and 
two or three helpers. They adjust the boiler so that the 
rivet is brought between the dies, and the riveter pulls the 



SHOP-PRACTICE. 425 

lever which controls the ram, and the outer die is driven 
against the rivet, forming the head and closing up the rivet 
in the joint. 

The holes are drilled about one sixteenth of an inch larger 
than the rivets. The pressure of the dies varies from 20 to 
70 tons, depending on the thickness of the plate ; enough to 
compress the rivet and fill the hole completely. The rivets, 
as they cool, shrink and draw the plates firmly together. 

Riveting-machines. — There are four types of riveting- 
machines used for boiler-work, depending on the method of 
moving the ram or plunger which carries the movable die. 
The motion may be derived from — 

1. A cam and toggle. 

2. A hydraulic cylinder, 

3. A combination of a hydraulic cylinder with a cam and 
toggle. 

4. A steam-cylinder. 

The cam and toggle riveter is now seldom used. In it 
the ram carrying the movable die is driven by a toggle-joint 
that'is closed by a cam, which in turn is driven by a belt and 
gearing. The adjustment for different thicknesses of plate is 
made by a wedge behind the ram, which can be set by aid of 
a screw. The pressure on the rivet is controlled by the elas- 
ticity of the frame of the machine and the setting of the 
wedge ; it cannot be regulated satisfactorily. 

The hydraulic riveter, in one form or another, is most com- 
monly used at the present time. With it a definite pressure 
can be applied to each rivet whatever the thickness of plate. 
Fig. 209 represents a hydraulic riveter with a reach of 96 
inches which can apply a pressure of 150 tons. It consists 
essentially of two heavy cast-iron levers or beams, bolted 
together near the middle and at the lower end. One beam 
carries the fixed die at its upper end ; the other carries the 
ram and hydraulic cylinder. The stroke of the ram can be 
adjusted and is controlled by a single lever. The ram moves 



426 



STEAM-BOILERS. 



in straight girders, and may apply an eccentric pressure with- 
out rotating or springing. 

Some hydraulic riveters have a hydraulic closing device 




Fig. 209. 
for holding the plates together while the rivets are driverio 
Even when furnished it is commonly not used. 

The reach of a riveting-machine is the distance from the 
dies to the bed-plate at the middle of the machine. It limits 
the width of plate that can be riveted by the machine. 

A portable hydraulic riveter is shown by Fig. 210, which 
has a reach of 12 inches and can apply a pressure of 75 tons. 



SHOP-PRACTICE. 



427 



It can be swung into position by a crane and can be turned to 
any angle by the gear at the trunnion. This type of ma- 
chine is used largely for bridge work; it is sometimes used 
for riveting nozzles, manhole-rings, brackets, and reinforcing- 
plates onto boilers. 

The power for working a hydraulic riveter is derived from 
either a steam-pump or a power-pump. A heavy geared 




Fig. 210. 
power-pump is shown by Fig. 211; it is run continuously 
and delivers water to an accumulator from which water is 
supplied to the hydraulic cylinder which moves the ram. 
The accumulator consists essentially of a loaded piston or 
plunger. Water is pumped into the cylinder of the accu- 



428 STEAM-BOILERS. 

mulator, and is drawn out by the hydraulic cylinder as needed. 
When the accumulator reaches the end of its stroke it closes 
a valve on the pipe from the pump so that it receives no 
more water; at the same time it opens a by-pass from the 
delivery to the suction of the pump which continues to rum 
but has at that time very little resistance to overcome. When 




Fig. 211. 

some water has been withdrawn from the accumulator the by- 
pass is closed and the valve on the delivery-pipe is opened. 
When a steam-pump is used there is a device for shutting off 
steam from the pump when the accumulator is near the end of 
its stroke, and letting it on again when more water is required. 
An accumulator, shown by Fig. 212, is loaded by scrap- 
iron in a plate-iron cylinder. Inside the plate-iron cylinder is 



SHOP-PRACTICE. 



429 



a cast-iron cylinder which is closed at the top and which moves 
on a fixed plunger. This plunger passes through a stuffing- 
box and is carried by a cast-iron bed-plate. When water is 




pumped into the cylinder through a passage in the fixed 
plunger, the whole weight of the cylinder, plate-iron casing, 
and scrap-iron load are lifted. The pressure required to do 



43° 



STEAM-BOILERS. 



this depends on the load ; it is the pressure which is exerted 
on the plunger of the hydraulic cylinder moving the ram. 
The frame of I beams at the sides forms a guide for the 
accumulator-cylinder and its load. 

Another form of accumulator, loaded with heavy cast-iron 
blocks and without any exterior guides, is shown by Fig. 213. 




Fig. 213. 



The hydraulic riveter with toggle and cam combines the 
simplicity of the cam-and-toggle machine with the advantage 
of a definite and determinable pressure on the rivet, which is 
the best feature of the hydraulic machine. The toggle bears 
against the ram at the front end, and against the plunger of a 
hydraulic cylinder at the back end. The cylinder is connected 
with an accumulator which is loaded to give the desired pres- 
sure on the rivet. Suppose that pressure to be 30 tons; then 



SHOP-PR A CTICE. 43 1 

when the cam closes the toggle, the rear end, resting against 
the hydraulic plunger, remains at rest, and the front end 
drives the ram and compresses the rivet till a pressure of 30 
tons is reached. When that pressure is reached the hydraulic 
plunger yields, forces water into the accumulator and raises 
the load on it. When the cam releases the toggle, the hy- 
draulic plunger moves forward and the load on the accumula- 
tor falls and drives water into the cylinder. The stroke of 
the hydraulic plunger may be very short, as the principal part 
of the stroke of the ram is made before the plunger yields. 
There is no loss of water except by leakage, which may be 
made up from time to time by a hand-pump. This machine 
gives a definite pressure on the rivet whatever the thickness 
of the plate, like the plain hydraulic riveter. It has no pump 
and the accumulator is smaller. If the plunger has a large 
area, the load on the accumulator need not be very great. 

Hand-riveting. — In a modern boiler-shop almost all the 
riveting is done by machine because it is cheaper and, espe- 
cially on heavy work, is more likely to be well done. There 
are, however, a good many rivets on any boiler that must be 
driven by hand. In such case the rivet, which may be heated 
entirely or at the point only, is thrust through the hole from 
within and is held up by a man inside, who has for this pur' 
pose a hammer or weight which weighs about 20 pounds on a 
long handle. He has also an iron hook which he hooks into 
a rivet-hole, and against which he gets a purchase to hold the 
rivet up while it is driven. Two men with hammers that 
weigh about 5 pounds drive the rivet, striking in turn. A few 
heavy blows are struck to close the joint and partially form 
the head, then the head is finished in the shape of a straight- 
sided cone with lighter hammers. If the rivet is long enough 
to form a good head, and if it is driven with care and skill, 
hand-riveting may be equal to machine-riveting. If the heads 
are ill-formed, or if they are too low, the work may be very 
inferior. 

Snap-riveting. — This method of riveting, which is espe- 



432 



S TEA M-B OILERS. 



cially convenient for driving rivets in contracted spaces, has 
some resemblance to machine-riveting. The rivet is thrust 
through the hole and held up from within the boiler. The 
joint is closed and the head is roughly formed by a few blows 
of a heavy hammer, then a snap or die is held on the rivet 
and driven with sledge-hammers. For large rivets the sec- 
tion of the snap should be a parabola, and the head should be 
relatively small in diameter and high, because this form causes 
the rivet to fill the hole better and makes sounder work. 

Tube-expanders. — The tubes are expanded into the tube- 
sheets to make a steam-tight joint, beginning at the least acces- 
sible end. They are commonly a little too long and are cut 
off at the projecting end by a tube-cutter. The tubes extend 
through the heads a slight amount, and are beaded over, after 
they are expanded, by a special tool. The expanders most 
commonly used are known as the Prosser and the Dudgeon 
expanders. 

The Prosser expander, represented by Fig. 214, is made up 




Fig. 214. 
of a number of steel segments held in place by a spring on a 
cylindrical extension of the segments. The acting part of the 
segments have the form to be given to the tube after it is 
expanded. The inside of the segments forms a straight hol- 
low cone into which a steel taper pin fits. The expander is 
forced into the tube and is expanded by driving in the pin 
with a hammer. This should be done gradually so as not to 
distress the metal of the tube tpo much, and the expander 
should be frequently slacked back and shifted part way round 
on account of the spaces between tne segments. 



SHOP-PRACTICE. 



433 

The Dudgeon expander, Fig. 215, has a set of rolls, three or 
more, in a frame. The rolls are forced out against the sides 
of the tube by driving in a taper pin. The pin and frame are 




CZ 



rotated as the pin is driven, and the rolls gradually force the 
tube against the tube-plate. 

Fig. 216 shows a self -feeding tube expander of the same type 
as the Dudgeon. 




Fig. 216. 



Although the two expanders accomplish much the same 
result, the action is different. The Prosser causes an abrupt 
stretching of the tube while the Dudgeon rolls the tube out grad- 
ually. One expander seems to be as good as the other. 

The expanded end of the tube conforms to the shape of the 
segments of the Prosser expander or to the shape of the rolls 
used in the Dudgeon. In general, the tube ends expanded by 
the two expanders will appear as in Figs. 217 and 218, which are 
drawn out of proportion to show the difference more clearly. 

An inexperienced person who may be using a tube expander 
for the first time may judge when a tube has been expanded 
sufficiently to be tight by watching the plate around the tube 



434 



STEAM-BOILERS. 



to see when fine hair-like cracks appear in the scale which covers 
the outside of the plate. 

When these lines show it means that the tube has been made 
to fill the hole and that the hole has begun to be stretched. 

After the tubes are expanded the ends are beaded over by a 
special tool known as a boot-tool. 

Beading adds a little to the holding power of a tube. Tube 
ends which are directly over a furnace, as is the case in vertical 





Fig. 217. 



Fig. 218. 



boilers like the Manning, should always be beaded. This bead- 
ing keeps the end of the tube in such cases from being eaten 
away by the fire. 

A vacuum may possibly be found in a boiler, if it is allowed 
to cool without admitting air. The Prosser method has an 
advantage in such case, when the tubes act as struts between 
the heads. The Dudgeon method will then act by friction 
only. The rollers might be shaped to give an expansion just 
inside the plate, instead of making them straight; there is, 
however, no evidence of trouble from this source in practice. 



SHOP-PRACTICE. 



435 



Calking. — The riveted seams of a boiler are made steam - 
tight by calking, which consists in driving the lower part of 
the planed edge forcibly against the plate beneath. Fig. 219 
shows the form of calking-tool used in hand-calking, the posi- 




FiG. 219. 

tion in which it is held, and the way the extreme edge of the 
plate is compressed against the plate beneath. The acting sur- 
face of the tool, which is about an men wide, is ground at an 
angle of somewhat less than 90 , and the edge is rounded 
slightly so that it will not cut the lower plate. The tool is slid 
along the under plate against the edge of the upper plate and 
struck with a hammer. If the tool is ground to a sharp edge 
and used carelessly, a groove may be cut in the under plate 
and serious injury may be done. 

A pneumatic calking-machine or tool is now used for 
doing most of the calking in boiler-shops. In general prin- 
ciple it resembles a rock-drill, and consists of a cylinder in 
wfiich works a piston and rod on the end of which is the 
calking-tool. Air is supplied for working the piston, at a 
pressure of 60 or 80 pounds, through a flexible tube. It 
makes about 1500 working-strokes a minute, 3/16 of an inch 
long. The calker, which is about 2J inches in diameter out- 
side and 15 inches long over all, is held by a workman who 
presses it slowly along the seam to be calked. The edge of 
the tool is well rounded so as not to injure the lower plate. 



436 STEAM-BOILERS. 

Work can be done four times as rapidly with the pneumatic 
calker as by hand. 

Cold-water Test. — After the boiler is calked it is tested 
to about once and a half the working pressure, with cold 
water. During the test the boiler is carefully watched to 
detect any notable change of shape or other sign of faulty 
design or construction, and important leaks are marked ; 
small leaks are of no consequence, as they will fill up with 
rust. Important leaks must be calked after the pressure is 
relieved ; if necessary, pressure may be applied again to see if 
they are stopped. 

If the boiler is examined by a boiler-inspector, he makes 
his inspection before the boiler is painted, and stamps certain 
letters on the head or over the fire-door to show that the 
boiler has passed inspection. 

Finally the boiler is painted and oiled ready for shipping. 



CHAPTER XII. 
BOILER-TESTING. 

The main object of a boiler-test is to determine the 
amount of water evaporated per pound of coal, or, more ex- 
actly, the amount of heat transferred to the boiler per pound 
of coal burned. For this purpose it is necessary to deter- 
mine : 

i. The number of pounds of water pumped into the boiler 
during the test. 

2. The number of pounds of coal burned, and the weight 
of ashes left. 

3. The temperature of the feed-water when it enters the 
boiler. 

4. The pressure of the steam in the boiler. 

5. The per cent of moisture in the steam discharged from 
the boiler. 

It is desirable to determine the conditions of combustion, 
such as the draught, the weight of air supplied per pound of 
coal, the composition of the products of combustion, and the 
temperature of the escaping flue-gases. It is also desirable to 
have determinations made of the composition of the coal and 
its total heat of combustion, but, as was explained in Chapter 
II, these determinations should usually be intrusted to a 
chemist and to a physicist. 

Water. — The best and most satisfactory way is to weigh 
the feed-water directly, in proper tanks or barrels on scales. 
There should be two barrels or tanks large enough so that the 
filling, weighing, and emptying may proceed without haste. 

437 



43 g STEA M -BOILERS. 

The scales should be adjusted and tested with a standard 
weight and should be known to be correct and sensitive. 
Good commercial platform scales are sufficient for this pur- 
pose. 

The weighing-barrels should be placed high enough to 
discharge into a tank or reservoir from which the feed-water 
is drawn by a pump or injector. This tank should hold more 
than both weighing-barrels, so that when it is about half 
empty an entire barrelful of water may be discharged into it 
without danger of overfilling it and wasting water. The bar- 
rels are emptied through large quick-opening lever- valves ; 
this point should receive attention, as any delay caused by 
small valves is ver}^ annoying. 

The weighing-barrels are filled either from a water system 
or by a special pump from a well or reservoir. When a direct- 
acting steam-pump is used, a quarter-inch by-pass should be 
carried from the delivery-pipe to the suction-pipe; the pump 
will then run slowly when the valves on the pipes leading to 
the weighing-barrels are shut ; when one of these valves is 
opened the pump starts away promptly, and it slows down 
again when the valve is shut. If a power-pump is used, it 
may be convenient to arrange so that it shall run all the time 
at full power, discharging into the well or reservoir when 
neither barrel is filling. 

Weighing water, though simple enough, requires care and 
intelligence, as any blunder will spoil the test. The observer 
should proceed systematically. He will naturally start with 
both barrels filled, weighed and recorded before the test 
begins. When the level in the feed-tank has fallen so that it 
can receive a barrelful of water he will open the discharge- 
valve from one barrel, which should be marked and designated 
as Barrel No. I. When that barrel is emptied, he will close 
the valve and weigh the barrel ; the weight empty is set down 
and subtracted from the weight full to get the weight dis- 
charged. The record of weights is kept in a table con- 



BOILER-TESTING. 



439 



taining columns for the name of the barrel, weights full, 
weights empty, weights discharged, and time at which dis- 
charged. The weight of the barrel empty must be taken 
each time, as the barrel will not drain completely in the time 
that can be allowed. 

Water may now be turned on to fill Barrel No. I, and 
Barrel No. 2 may be emptied, as occasion demands. Then 
one barrel may be filling when the other is emptying, and the 
work may proceed rapidly but without confusion. The errors 
that a novice is liable to are either to forget to record the 
weight of a barrelful of water, or to empty a barrel that has 
not been weighed. 

It is convenient and almost necessary to have some sort of 
an index or telltale to show the water-weigher where the 
water-level is in the feed-tank. For this purpose we may use 
a float, with a string that runs up over a pulley and is kept 
taut by a small weight moving over a scale, which is placed 
in front of the weighing-barrels. This float is not used to 
determine the level of the water in the feed-tank at the begin- 
ning and end of the test. 

At the beginning of the test the level of the water in the 
feed-tank is marked, and at the end of the test the level is 
brought to the same mark, so that all the water delivered by 
the weighing-barrels is drawn out of the feed-tank by the 
feed-pump. A good way of marking the water-level is to 
fasten to the side of the tank a piece of wire bent into a hook, 
with its point projecting slightly above the water-level. This 
hook will commonly be placed in position before the test 
begins, and the tank will be filled up to the level so marked 
before water is drawn from the feed-tank. 

If water cannot be weighed directly, it may be measured 
in tanks of known capacity which are alternately filled and 
emptied. Or the water may be measured by a good water- 
meter, which must be tested under the conditions of the test 
to determine its error. Care must be taken to keep the meter 



44-0 STEAM-BOILERS. 

free from air or it will record more than the amount of 
water which actually passes. Boiler-tests on steamships can 
scarcely be made without using meters. 

At the time when the test begins, the water-level is noted 
at the water-glass, and at the end of the test the water-level 
is brought to the same place. The best way is to fix a 
wooden scale near the water-glass and record the height of the 
water above an arbitrary point on the scale. Sometimes a 
string is tied around the glass at the water-level when the test 
is started ; in such case the distance of the string from some 
fixed point on the fittings of the water-glass must be recorded, 
so that the string can be replaced if it happens to be moved 
or if the glass tube breaks. If the water is not brought 
exactly to the same level at the end as at the beginning of the 
test, the difference is noted and allowance is made. It has 
already been pointed out that the apparent height of the 
water depends to a certain extent on the rate of vaporization 
and on the rapidity of circulation in the boiler; consequently 
the boiler must be making steam at the same rate at the times 
when the water-level is observed for beginning and ending the 
test. 

All pipes leading water to or from the boiler, except the 
feed-pipe, must be disconnected. Steam may be taken for 
any purpose and through any pipe, so far as the boiler-test is 
concerned. 

Frequently the steam used by an engine is determined by 
weighing the feed-water for a boiler which is used exclusively 
for that engine. If the boiler is fed by an injector, the steam 
for running the injector should be taken from the boiler, for 
it will be condensed by the feed-water and returned to the 
boiler. A very small amount of the heat (less than two per 
cent) in the steam supplied to an injector is used in pumping 
the feed-water; the remainder is used in heating the feed- 
water and is returned to the boiler. The temperature of the 
feed-water must be taken before it goes to the injector. If the 



BOILER-TESTING. 441 

boiler is fed by a direct-acting steam-pump, that pump should 
be run with steam taken from some other source. If that 
cannot be done, then the steam used by the pump must be 
determined and allowed for, unless the exhaust from the 
pump can be turned into and condensed by the water in the 
feed-tank, in which case the pump is in the same condition 
as an injector. The best way of determining the amount of 
steam used by a steam-pump is to condense it in a small sur- 
face condenser, and to collect and weigh the condensed water. 
Or the steam may be run into a barrel filled with cold water, 
which is weighed before and after steam is run in. This 
method requires that the barrel shall be emptied when the 
water begins to vaporize, and filled afresh with cold water. 
Steam used by a calorimeter for determining the amount of 
water in steam must be ascertained also; the methods will be 
given in connection with a description of the instruments. 

Coal and Ash. — The coal required during a boiler-test 
should be brought in as required in barrows; it may be fired 
from the barrow or dumped and fired from the floor. The 
barrow should be weighed full and empty, and the difference 
should be recorded together with the time ; the latter to serve 
as a check on the record and make sure that a barrow-load is 
not neglected. The weight of the barrow is usually the same 
throughout the test. Any coal left unburned is weighed back 

It is essential that the condition of the fire shall be tne 
same at the beginning and at the end of the test. There are 
two methods in vogue for trying to attain this result ; if the 
test is 24 hours long or more, the condition of the fire is esti- 
mated by its appearance; if the test is 10 or 12 hours long, 
the test is started and stopped with the grate empty. These 
are for tests of factory boilers with a combustion of 15 to 20 
pounds of coal per square foot of grate per hour. For tests 
on marine or locomotive boilers, where the rate of combustion 
may be twice or five times as rapid, the duration of a test 
may be correspondingly reduced. 



44 2 STEAM-BOILERS. 

Coal in solid mass will weigh 70 or 80 pounds to the cubic 
foot; when lying on a grate it will weigh 50 or 60 pounds. 
It is difficult to estimate the thickness of the bed of coal on a 
grate nearer than two inches. But a layer of coal two inches 
thick will weigh 8 or 10 pounds, which is about half the rate 
of combustion for a factory boiler. If a test is only ten hours 
long, the error resulting from a wrong estimate of the thick- 
ness of the fire may readily be five per cent. If the test lasts 
twenty-four hours, the error will probably not be more than 
two per cent, provided a proper method is used. 

If the condition of the fire is estimated at the beginning 
and end of the test, the fire should be cleaned and freed from 
ashes and clinker shortly before the test begins, and should 
then be spread in rather a thin even layer of clean glowing 
coal. Its height above the grate should be estimated with 
reference to some mark in the furnace that can be recognized 
readily. Just as long before the end of the test the fire 
should be cleaned and levelled in the same manner, and the 
thickness should be estimated with reference to the mark 
chosen at the beginning. The fireman is sure to have a clean 
bright fire at the beginning of the test, but he is apt to have 
a fire with much the same appearance that is half clinker at 
the end. The error from estimation may be very serious in 
such case, even though the test is 24 hours long. 

If the test is started and stopped with the grate empty, 
the boiler must be brought into good working condition about 
an hour before the test is to start, with all the brickwork 
thoroughly heated. The fire is allowed to burn low, and the 
steam-pressure is maintained by reducing the draught of 
steam from the boiler. Twenty or thirty minutes before the 
test starts, the fire is drawn or dumped and the grate and ash- 
pit are cleaned out. A new fire is started with wood, and 
coai is thrown on as soon as the wood is well alight. The 
time when coal is thrown on is counted as the beginning of 
the test. If the steam-pressure falls while the fire is drawn, 



BOILER-TESTING. 443 

the stop-valve may be nearly or quite closed to keep it from 
falling much below the working-pressure. Toward the end of 
the test the fire is allowed to burn low, and at the end of the 
test it is drawn out on the boiler-room floor and quenched with 
as little water as may be, not enough to leave it wet. The 
unburned coal is picked out by hand and weighed back, the 
clinker and ashes are separated and weighed together with the 
clinker withdrawn during the test and the ashes in the ash-pit. 

If any appreciable amount of coal falls through the grate, 
a sample from the ash-pit may be picked over by hand to es- 
timate the proportions of unburned coal in the ash. The coal 
in the ash is allowed for in calculating the per cent of ash in 
the coal, but is not added to the coal weighed back, for there 
is no way of burning coal thus lost through the grate. When 
a test is started with a wood fire, more or less coal is apt to 
fall through the grate in starting. This is drawn from the pit 
and fired over again. 

It is customary to allow the fire to burn low before draw- 
ing the fire at the end of the boiler-test, both because it brings 
the fire more nearly to the condition at the beginning, and 
because it is a hard and unpleasant job to draw a thick fire. 
But the fire should be maintained at its normal condition 
until the end of the test approaches, and should be a good 
fire when drawn. Extraordinary results may be obtained by 
allowing the fire to burn nearly out at the end of the test, a 
very considerable amount of steam being formed by heat 
given out by the boiler-setting. It is unnecessary to say that 
such results are entirely misleading. 

The wood used for starting the fire is weighed and allowed 
for on the assumption that a pound of wood is equivalent to 
0.4 of a pound of coal. The total weight of wood used is not 
large. 

Temperature of Feed-water — The temperature of the 
feed-water is taken by a thermometer in a cup filled with oil, 
screwed into the feed-pipe close to the check-valve. If the 



444 STEAM-BOILERS. 

temperature varies, it may be read every five minutes: if it 
is found to be steady, less frequent intervals will do. 

Pressure of Steam. — The steam-pressure must be very 
nearly the same at the beginning and end of a test, and 
should remain nearly constant throughout the test. Read- 
ings are commonly taken every fifteen minutes, but the fire- 
man should be required to keep the pressure nearly constant 
at all times. 

The steam-pressure is taken by a spring-gauge like that 
shown by Fig. 139 on page 345. The gauge should be 
compared with a mercury column or a standard gauge both 
before and after the test, and a correction should be applied 
if necessary. If the pipe carrying pressure to the gauge fills 
up with water, allowance for the pressure of that column of 
water must be made. Each foot of water will give a pressure 
of about 0.43 of a pound per square inch. 

The reading of the barometer should be taken two or 
three times during a test. The reading in inches of mercury 
can be reduced to pounds per square inch by multiplying by 
the weight of a cubic inch of mercury, which is about 0.491 
of a pound. 

Very commonly the pressure of the steam is obtained 
indirectly by aid of a thermometer set in the steam-pipe. 
The absolute pressure corresponding to the temperature is 
then obtained from a table of the properties of saturated 
steam. The thermometer is readily standardized, and is not 
so likely to become unreliable as a steam-gauge. 

Most vertical boilers and some water-tube boilers give 
superheated steam ; in such case there should be both a 
thermometer and a gauge on the steam-pipe, to indicate tem- 
perature and pressure. The excess of the temperature by 
the thermometer above that corresponding to the absolute 
pressure of the steam, as found in a table of properties of 
steam, is the degree of superheating. 

Specific Heat of Superheated Steam. — The mean value 



BOILER-TESTING. 445 

of the specific heat of superheated steam is given in Chapter II. 
The value is commonly represented by c p . The value increases 
with the pressure and at the same pressure decreases as the super- 
heat increases. 

For example, let the pressure by the gauge be 65.3 
pounds, and let the temperature be 350 F. by the thermom- 
eter. The absolute pressure corresponding to 65.3 pounds 
is 80 pounds, at which saturated steam has the temperature 
of 3 12°. I F. The superheating is consequently 

350 F. — 3i2°.i F. = 37 . 9 F. 

The heat due to the superheating is 

o.53 X 37-9 = 20.1 B. T. U. 

When the steam is superheated, the formula for equivalent 
evaporation is changed from the form given on page 148 to 

c P (t s — t) + r + q — q 

w 7 , 

9697 

in which t t represents the actual temperature of the super- 
heated steam, and / is the temperature corresponding to the 
absolute pressure of the steam determined from the reading 
of the gauge. 

Priming. — A boiler which has sufficient steam-space and 
free water-area will deliver steam which contains less than 
two per cent of moisture. 

Professor Denton* has pointed out that a jet of steam 
blowing into the air from a petcock will give a characteristic 
blue color if there is less than two per cent of water in the 
steam. If there is more than two per cent of moisture, the 
jet will be white. Since steam seldom contains less than 
one per cent of moisture under the usual conditions of 
ordinary practice, it is possible by this method to estimate 
the condition of steam with a probable error of one per cent. 

* Trans. Am. Soc. Mech. Engs., vol. x. p. 349. 



446 



STEAM-BOILERS. 



The most ready way of determining the condition of 
steam is by the aid of a throttling-calorimeter, devised by 
Professor Peabody,* which depends on the fact that the total 
heat of steam increases with the pressure, so that dry steam be- 
comes superheated when the pressure is reduced by throttling. 
If the steam is only slightly primed, superheating will still 
take place, and the amount of priming can be determined 
from the temperature and pressure of the steam after it is 
throttled. If there is much moisture in the steam, it fails to 
superheat. 

A good form of this apparatus is shown by Fig. 220, 
consisting of a reservoir A to which the 
steam to be tested is admitted through 
a <half-inch pipe b with a throttling-valve ft . 
near the reservoir. The steam flows 
away through an inch pipe d. At f is 
a gauge for measuring the pressure, and 
at c there is a deep cup for a ther- 
mometer to measure the temperature. 
The boiler-pressure may be taken from 
a gauge on the main steam-pipe near 
the calorimeter. It should not be taken 
from a pipe in which there is a rapid 
flow of steam as in the pipe b, since 
the velocity of the steam will affect 
the gauge-reading, making it less than 
tne real pressure. The reservoir is 
wrapped with hair-felt and lagged with wood to reduce radia^ 
tion of heat 

When a test is made the valve on the pipe d is opened 
wide (this valve is frequently omitted), and the valve at b is 
opened wide enough to give a pressure of five to fifteen 
pounds in the reservoir. Readings are then taken of the 




Fig. 220. 



* Trans. Am. Soc. Mech. Engs., vol. x. p. 327. 



BOILER-TESTING. 



447 



boiler-gauge, of the gauge at f % and of the thermometer at e. 
It is well to wait about ten minutes after the instrument is 
started before taking readings, so that it may be well heated. 

The method of calculation can be readily understood 
from the following 

Example. — The following are the data of a test made 
with a throttling calorimeter: 

Pressure of the atmosphere 14.8 pounds. 

Pressure by the boiler-gauge 69.8 " 

Pressure by the calorimeter-gauge 12.0 " 

Temperature in the calorimeter 268°.2 F. 

The absolute pressure in the boiler was 

69.8 -f- 14.8 = 84.6 pounds, 

at which the heat of vaporization is 896.8 B. T. U. and the 
heat of the liquid is 286.2 B. T. U. So that with x part of 
a pound steam (and 1 — x priming) the heat in one pound of 
moist steam was 

896.8*+ 286.2, 

in which x was to be determined. The absolute pressure in 
the calorimeter was 

12 + 14.8 = 26.8 pounds, 

at which the temperature was 243 °.9 F., and the total heat 
was 1 161.3 B. T. U. The heat due to superheating was 

o.55(268°.2 - 243°.9) = 13.4 B. T. U., 

and the heat in one pound of steam in the calorimeter was 

1161.3 + 13.4= 11747B.T.U. 

But the process of throttling neither adds nor subtracts heat, 
consequently 

896.8* 4- 286.2 = 1174.7 
or x = 0.990, 



448 STEAM-BOILERS. 

and the priming was 

100(1 — 0.990) = 1. 00 per cent. 

The calculation can be conveniently expressed by an equa- 
tion in which r and q are the heat of vaporization at the abso- 
lute boiler-pressure, and \ and t x are the total heat and the 
temperature at the absolute pressure in the calorimeter, all 
taken from a table of properties of steam ; while t s is the 
temperature of the superheated steam in the calorimeter. 
Then 

h+cJt s —h)—q 

x = - 

r 

It has been found by experiment that no allowance need 
be made for radiation from the calorimeter if made as de- 
scribed, provided that 200 pounds of steam are run through 
it per hour. Now this quantity will flow through an orifice 
one fourth of an inch in diameter under the pressure of 70 
pounds by the gauge, so that if the throttle-valve be replaced 
by such an orifice the question of radiation need not be con- 
sidered. In such case a stop-valve will be placed on the pipe 
to shut off the calorimeter when not in use; it is opened wide 
when a test is made. If an orifice is not provided, the 
throttle-valve may be opened at first a very small amount 
and the temperature in the calorimeter noted after a few min- 
utes; the valve may be opened a trifle more, whereupon the 
temperature will usually rise, showing too little steam used. 
If the valve is opened little by little till the temperature stops 
rising, it will then be certain that enough steam is used to 
reduce the error from radiation to a very small amount. 

Various modifications of the throttling-calorimeter have 
been proposed, mainly with a view of reducing its size and 
weight. Almost any of them will prove satisfactory in prac- 
tice, but some will be found to be liable to error from radia- 



BOILER-TESTING. 



449 



tion or from the fact that there is not sufficient opportunity 
for the steam to come to rest and properly develop the super- 
heating due to throttling. One great advantage of this 
instrument is that ordinary care with ordinary gauges and 
thermometers gives sufficient accuracy. For example, with 
IOO pounds absolute boiler-pressure and with atmospheric 

pressure in the calorimeter, an error 
of half a degree by the thermometer, 
or half a pound by the boiler-gauge, 
or a third of a pound by the calo- 
rimeter-gauge will each give an error 
of one-tenth of a per cent in the 
priming. 

If steam contains more than three 
per cent of priming, the amount of 
moisture can be determined by a good 
separator, which will remove nearly 
all the moisture. It remains then 
to measure the steam and water sep- 
arately. The water may be best 
measured in a calibrated vessel or 
receiver, while the steam may be 
condensed and weighed, or may be 
gauged by allowing it to flow through 
an orifice of known size. A form 
of this instrument devised by Professor Carpenter * is shown 
by Fig. 221. 

Steam enters a space at the top which has sides of wire 
gauze and a convex cup at the bottom. The water is 
thrown against the cup and finds its way through the gauze 
into an inside chamber or receiver, and rises in a water-glass 
outside. The receiver is calibrated by trial * so that the 
amount of water may be read directly from a graduated scale. 




Fig. 22i. 



* Trans. Am. Soc. Mech. Engs.. vol. xvil p. 608. 



450 STEAM-BOILERS. 

The steam meanwhile passes into the outer chamber which 
surrounds the inner receiver, and escapes from an orifice at 
the bottom. The amount of steam may either be calculated, 
by a method to be explained, from the diameter of the orifice 
and the pressure of the steam, or it may be condensed and 
weighed or measured. The latter is the more accurate way, 
and it has the advantage that then there is no error from 
radiation, for the inner receptacle is well protected by the 
outer chamber, and condensation in the outer chamber is 
collected and weighed with the steam. If the instrument is 
well wrapped and lagged, and if a sufficient quantity of steam 
is used, then the error from radiation can be neglected, just 
as was found to be the case with the throttling-calorimeter. 
This instrument, for want of a better name, is called a separator 
calorimeter; it is a question whether either it or the throttling- 
calorimeter are properly calorimeters at all, and whether it 
would not be better to call both priming-gauges. 

It is customary to take a sample of steam for the calori- 
meter or priming-gauge through a small pipe leading from 
the main steam-pipe. The best method of securing a sample 
is an open question ; indeed it is a question whether we ever 
get a fair sample. There is no question but that the com- 
position of the sample is correctly shown by either of the 
priming-gauges described. It is probable that the best way 
is to take steam through a pipe which reaches at least half- 
way across the main steam-pipe, and which is closed at the 
end and drilled full of small holes. It is better to have the 
sampling-pipe enter the steam-pipe at the side or at the top of 
the main, so that any water that may trickle along the bottom 
of the main shall not enter the calorimeter. Again, it is better 
to take a sample from a pipe through which steam flows 
upward. The sampling-pipe should be short and well wrapped 
to avoid radiation. 

If the steam from the boiler can be wasted during the test, 
then the entire steam delivered by the boiler may be passed 



BOILER-TESTING. 



451 



through a large priming-gauge, and the difficulty of getting a 
sample may be avoided. 

Flow of Steam. — It has been shown by Rankine * that 
the flow of steam through an orifice into the atmosphere may 
be represented by an empirical equation, 

in which Wis the number of pounds of steam per second, A 
is the area of the orifice in square inches, and p is the absolute 
pressure of the steam. This equation, which has already 
been mentioned in connection with safety-valves, can be 
applied only when the absolute steam-pressure is more than 
double the pressure of the atmosphere; that is, the pressure 
of the steam must be 15 pounds by the gauge, or more. 
Experiments made in the laboratory of the Massachusetts 
Institute of Technology f show that this equation is liable to 
an error of about T 5 o per cent, but this error may be deter- 
mined by direct experiment for a given orifice under various 
pressures, and then a correction can be applied which will 
reduce the error to a fraction of one per cent. 

It appears then that the use of an orifice to determine the 
amount of steam in Professor Carpenter's separator priming- 
gauge is at least questionable unless direct experiments are 
made to determine the correction to be applied. On the 
other hand, the amount of steam used by a throttling prim- 
ing-gauge may be very properly determined by allowing i 4 
to flow through an orifice, since the total amount of steam 
used by the calorimeter is small. 

The same equation may be used for calculating flow of 
steam from one reservoir to another provided that the pres 
sure in the second reservoir is less than half that in the first 



* The Engineer, vol. xxvn. p. 359, 1869. 
f Trans. Soc. Am. Engs., vol. XI. p. 187. 



452 STEAM-BOILERS. 

reservoir. This allows us to gauge small quantities of steam 
used for any purpose, at a pressure that is less than half the 
boiler-pressure; for example, for running a steam-pump. A 
convenient arrangement for gauging the flow of steam in an 
inch pipe consists of a reservoir three feet long, made up of 
three-inch piping, and fittings divided at the middle by a 
brass plate through which there is an orifice of proper size. 
If the pipe carries steam at ioo pounds absolute, at a velocity 
of ioo feet a second it will deliver 

nd 2 3.1416 X (tV) 2 

— X 100 = — ^- X 100 = o.5455 

4 4 

cubic feet per second. The density or weight of one cubic 
foot of steam at 100 pounds absolute is 0.2271 pounds. So 
that the pipe will carry 

0.5455 X 0.2271 = 0.124 

of a pound of steam per second. If this weight is put for W 
in Rankine's equation, and if A is replaced by £ nd*, we 
shall have 

nd* X 100 
0.124= , 

* 4 x 70 



or 



d 



_ /0.124 

" V 3. hi 



X 4 X 70 _ I 



6 X 100 3 



of an inch, nearly, for the diameter of the orifice for gauging 
the flow of steam. With an orifice of approximately the 
right size, the flow of steam may be regulated by a valve 
below the gauging device; for example, by the throttle-valve 
of the pump. 

Flue-gases. — At frequent intervals samples of flue-gases 
should be taken from various places, such as back of the 
bridge, from the uptake, and from the chimney. These sam- 



BOILER-TESTING. 



453 



pies are analyzed as soon as may be by Orsat's apparatus, as 
described on page 85. 

Though not commonly done, it would be well if a con- 
tinuous sample could be taken in a reservoir from which 
samples for analysis could be taken at intervals. 

Draught-gauge. — The draught given by a chimney is 
seldom more than an inch or an inch and a half of water. It 
can be measured roughly by a simple U tube filled with water. 
An instrument for accurate determinations of draught should 
be at once simple and certain in its action. 

The draught-gauge shown by Fig. 222, devised by Prof. 




Fig. 222. 



Miller, has been used with satisfaction for this purpose. It 
consists of two pieces of three-inch brass pipe connected by a 
half-inch pipe at the bottom. One of the pipes is closed at 
the top and can be connected to the chimney by a small pipe 
with a valve as shown. The other piece of brass pipe is open 
and has a hook-gauge, reading to 1/1000 of an inch, suspended 
in it. In preparing for a reading, the closed tube or leg is 



454 



STEAM-BOILERS. 



shut off from the chimney and opened to the atmosphere; the 
water then stands at the same height aa, a'a\ in both legs. 
The closed leg is now shut off from the air and connection is 
made with the chimney, whereupon the level falls to bb in the 
open leg and rises to b'b' in the closed leg. As the two legs 
have exactly the same internal diameter, the fall ab is half the 
draught, measured in inches of water. The hook-gauge is set 
to the level aa when the closed leg is open to the air, and to 
the level bb when it is connected to the chimney. The differ- 
ence of the readings multiplied by 2 is the draught in inches 
of water. The reading by the hook-gauge can readily give an 




accuracy of 1/1000 of an inch, which is sufficient for this pur- 
pose. 

A simple form of differential draught gauge is shown by 
Fig. 223. The gauge must be set level and the level of liquid 
brought to zero by introducing or removing liquid with a 
dropper. Knowing the inclination of the tube in which the 
water moves the graduations of the scale may be calculated. 

Pyrometers. — The determination of high temperatures, as in 
flues and chimneys, is difficult and uncertain. Most commer- 
cial pyrometers, depending on the unequal expansion of metals, 
are unreliable if not misleading; not only is the scale of such a 
pyrometer likely to be incorrect, but the zero of the scale is liable 
to change during use. 

The Chatelier pyrometer has been used with satisfaction at 



BOILER-TESTING. 455 

the Massachusetts Institute of Technology for measuring tem- 
peratures in flues and chimneys. It consists essentially of a 
thermoelectric couple made by joining the ends of two wires, 
one of platinum and the other of platinum alloyed with 10 per 
cent of rhodium. All but about 4 inches of the wire at the 
junction is incased in fire-clay inside an iron pipe about 4 feet 
long. From the wires of the pyrometer connection is made to 
a sensitive galvanometer in a separate observing-room. The 
deflection of the galvanometer is indicated by a ray of light re- 
flected from a mirror on the needle and moving over a graduated 
scale. The scale is set to read zero when the junction of the 
wires is at the temperature of the atmosphere. The junction is 
then immersed successively in baths of substances which melt 
at various high temperatures, such as sulphur and naphthalene. 
The readings of the ray of light when the juncture is in such 
baths fix known points on the arbitrary scale from which in- 
termediate temperatures may be estimated directly. It is con- 
venient to use a curve for this purpose with scale-readings for 
abscissae and with corresponding temperatures for ordinates. 
After the scale is determined the pyrometer may be intro- 
duced into the place or places where temperatures are to be 
measured, and readings are taken from which the tempera- 
tures are determined by interpolation on the curve just de- 
scribed. 

Air-supply. — The air for a furnace may be made to enter 
through a temporary mouthpiece fitted to the ash-pit doors. 
This mouthpiece may be of galvanized iron, circular in sec- 
tion and about 3 feet long. Its cross-section should have an 
area equal to that of the door or doors leading to the ash-pit. 
The velocity of the air passing through the mouthpiece can be 
measured by an anemometer. The area of the mouthpiece 
multiplied by the velocity in feet per second gives the volume 
of air supplied to the ash-pit in cubic feet per second. From 
this may be calculated the volume and weight of air supplied to 
the ash-pit per hour or for the entire test; which weight divided 



456 STEAM-BOILERS. 

by the total coal consumption gives the air per pound of coal 
burned. 

It should be noted that the anemometer is liable to an error 
of from 2 to 5 per cent, and further that air entering through 
the fire-doors and elsewhere than through the ash-pit is not 
measured. 

Sample Test. — The test given on page 457, made at the 
Massachusetts Institute of Technology, may serve as an ex- 
ample of a convenient arrangement for reporting the data and 
results of a boiler test. 

The average pressure of the air and of the steam in the 
boiler are liable to vary slightly during the test; the average 
pressures were obtained from readings taken at regular intervals 
during the test. The same may be said of the temperature of 
the feed-water. 



BOILER-TESTING. 



457 



EVAPORATIVE TEST ON BOILER PLANT. 

Date, ^ec.30, /go/, 4 P.M., to Jan. 4,/qo2, 8A *M. 



DATA. 
Brief description of method of testing : 

The feed-water was weighed and delivered to a barrel connected to the suction of the feed- 
pump. 

Coal was weighed in 300 lb. lots as fi red. 

Calorimeter readings were taken every hour. 

Flue-gas samples every half hour; all other readings quarter hours. 

Fires were cleaned two hours before starting and same time before the ending and twice 
during twenty-four hours. 

Blow-off pipes were blanked. 
Brief description of boilers: 

Boilers No. 4 and No. 5, horizontal multitubular, 16' long-. 

Diameter of shed = bo" ; 84 3" tubes /b' long. 

Grates bo%" X 6/}&" {Herringbone grates). 

Boilers No. b and No. 7 are furnished with Hawley down-draught furnaces : otherwise 
they are the same as Boilers No. 4 and No. 5. 



Duration of test ......... 


/T2 


hours. 


Barometer .... 






29.96 inches. 


I4.70 


.pounds, 
pounds. 
v.o° F 


Boiler pressure (gauge) 
Temperature of the air 
Temperature of feed water 
Temperature of steam 
Degrees of superheat 
Quality of steam, dry steam unity 
Kind of coal used .... 
Moisture in coal, by drying test 
Total water fed to boilers 


. insi 


de bl 


loo.q 
/0 F.; outside * 


24 


'4° C. 


75-9° F 
.... ° F 






C 

c., 






p 






-991 
Neiv River. 

*'3 percent 
746,457 pounds. 


Type of Boiler and Number of 
Boiler. 


a 

ffic/) 




2 8 

OS 
in 


££2 


■3 "2 

O u 


•3.0 

41 


c v 

<0 


£ J 




1,113 


25-9 


42. qb-/ 


23,400 


23-096 


1-449 


21.647 


No. 5. 


1,113 


25-9 


42. qb-/ 


22, /So 


2t,8q2 


1.815 


20,077 


No. b. 


i,/bb 


20.3 


57-45-1 


20.oqo 


/q,82q 


2-055 


17-774 


»« " No. 7. 


i./bb 


20.3 


57-45-1 


18.973 


/8.72b 


2,003 


ib,723 









































































Totals .... 


4-558 


92.4 


49-33-1 


84-643 


83-544 


7-322 


7b,222 



Total ash and clinker in per cent, total dry coal 



8.76 



458 



STEAM-BOILERS. 



EVAPORATIVE TEST ON BOILER PLANT. 



= 1.7, Ash = 7.5. 



14,555 B.T.U. 



875W pounds. 
10.48 p min ri<;. 
"•4Q pounds 

__ZlZH_pcunds. 
S ' lS pounds. 



RESULTS. 
Chemical analysis of coal H i° = °-'> ? = °°-°< H = °-5, S = a-** 
Heat of combustion of coal as fired ..... 

Total equivalent evaporation from and at 212 F. . . . 

Equivalent evaporation from and at 212° F. per pound of dry coal . 
Equivalent evaporation from and at 212 F. per pound of combustible 
Equivalent evaporation from and at 212 F. per square foot of heating 

surface per hour. .... 

Coal burned per square foot of grate surface per hour 
Boiler horse-power developed, A. S. M. E. rating 
Maximum assumed possible error of test . 
Air per pound of coal from analysis of flue gases 
Air required per pound of coal from the formula I 12 C -+- 36 \H — —j 
Excess air supplied ..... 
Heat carried off by flue gases per pound of coal 
Heat taken up by water in boiler per pound of coal 
Total heat furnished per pound of coal 
Heat radiated per pound of coal . 
Heat carried off by flue gases 
Thermal efficiency of boiler plant . 
Heat lost by radiation, etc. . 



226.5 
°&7 per cent. 

3°'7 pounds. 

IO -9 pounds. 

182 per cent. 



2,485 B.T.U. 

1 0,033 B.T.U. 

14,555 B.T.U. 

2,037 B.T.U. 

17 ■ 1 per cent. 

68. q per cent. 

I4-Q per cent. 







GAS ANALYSIS: 


Per cent by volume. 










CO a 


o 2 CO 


Bet. bridge wall 


co 2 


o 2 


CO 


Ash-pit . 






and back end 








Above grate . 






Back end . . . 








At bridge wall 






Uptake 


6.4 


12.0 


O.I 



DRAUGHT AND TEMPERATURES. 



Setting. 



Ash-pit 

Above grate 

At bridge wall 

Between bridge wall and 

back end . 
Back end . 
Uptake 



Inches of 
Water. 



F. 



301 



Stack. 



feet above grate. 



Inches of 
Water. 



F. 



Remarks: 

The coal was of poor quality. Fires were hard to clean, as there were bad clinkers. 

The firing was good. 



BOILER-TESTING. 459 

Total equivalent evaporation from and at 212 F.: 

(.99ir-\-q) at absolute ^boiler-pressure is 1181.7 B.T. L'. 

(q) at temperature of feed-water (75. 9 F.) is 44.0 " 

Heat necessary to vaporize a pound of feed-water 

into steam primed .9 per cent is 1137. 7 B.T.U. 

.137-7 X746 457 = 87577opounfe 
969.7 is the latent heat of steam at 212 F. 

Equivalent evaporation from and at 21 2 F. per pound of dry coal : 

87^770 

n = 10.48 pounds. 
83544 



Equivalent evaporation from and at 21 2° F. per pound of dry 

combustible : 

8 7577° 

-^—.s 11.49 pounds. 



Equivalent evaporation from and at 212 F. per square foot of 
heating surface per hour: 

8 7577° •. 

-^-^ =1.72 pounds. 

4558X112 v 



Coal burned per square foot of grate surface per hour 

_?il43_ = 8 . l8 pounds. 
92.4 X 112 



460 STEAM-BOILERS. 

Boiler horse-power developed (A.S.M.E. rating). (See page 218.) 

"37-7 X 746457 



112 x 33 + 70 



226.5 



Maximum assumed possible error of test. — It is assumed that an 
error of one inch may be made in estimating the thickness of each 
fire at the beginning and at the end of the test and that these errors 
are cumulative, thus making the total error two inches over the entire 
grate. For soft coal the weight of a cubic foot is about 48 pounds. 

92.4 X 48 X j 2 — 739- 2 pounds error. 
739.2 X 100 



84643 



0.87 per cent. 



Thermal efficiency of boiler plant. — This is the ratio of the heat 
taken up by the water in the boilers per pound of coal fired to the 
heat given up by a pound of coal as fired. 

H37.7X746457XIOO 

— -^—. = 68.9 per cent. 

14555 X 84643 



Air per pound of coal from analysis of flue-gases. (See pages 
88, 8 9 , 90.) 

C0 2 = 6.4X22 = 140.8; T 3 T X 140.8 = 38.4 C 

2 = 12.9 X 16 = 206.9 

CO = 0.1X14= i-4j fX 1.4= 0.6 C 

348.6 39-oC ' 

348.6 — 39 = 309.6 o 2 . 



BOILER-TESTING. 461 

— ^1- = 7.94 pounds of oxygen per pound of carbon. 
39 

'—^1 — 34. 2 pounds of air per pound of carbon. 
.232 

As the coal is 90 per cent carbon, the air per pound of coal is 
30.8 pounds. 



Air required per pound of coal from formula : 
i2C-l-36^H— -J = 12 X .9 + 36^.005 + '-^^ 1 = 10.9 pounds 



Excess of air supplied- 

(30.8 — 10.9)100 
10.9 



182 per cent. 



Heat carried off by the gases per pound of coal. — There were 30.8 
pounds of air and .9 pounds of carbon, making 31.7 pounds of gas for 
each pound of coal burned. 

The proportion of the gases by weight may be figured from the 
flue-gas analysis : 

C0 2 6.4 X22- 140.8 

2 12.9 x 16 = 206.9 

CO 0.1 X 14 = 1.4 

N 2 80.6 x 14 = 1128.4 

100. o 1477.5 

■ — X 31.7 =" 3-02> the weight of CO 

J477-5 

— X 31.7 = 4-44> the weight of O 

J477-5 

— - X 31.7 = 0.03, the weight of CO 

J 477-5 

- X ^1.7 = 24.21, the weight of N, 
1477-5 



46 2 STEA M-BOILERS. 

The temperature of the flue was 391 F., while the air in the boiler- 
room was 6i° F.; a difference of 330 F. 

Multiplying the weights of the gases by their specific heats and by 
the number of degrees increase in temperature. (See pages 75-93.) 

Weight. S P eci f c Temperature BT 

° Heat. Increase. 

CO2 3.02 .2169 330 216.2 

2 4-44 .2175 330 318.6 

CO 03 .2450 330 2.4 

N 2 24.21 .2438 330 1947-8 

2485.0 

No allowance has been made for the moisture in the coal or for 
the moisture in the air. This moisture might amount to 90 or 95 
heat-units in a total of 2500. 

A much simpler method of finding the heat carried off by the flue- 
gases, although not as accurate as the one given above, is sufficiently 
accurate for most work. 

There are 31.7 pounds of gas per pound of coal; call the average 
specific heat of flue-gas .235. The heat carried away is then 

31. 7X330X. 235 = 2474, 

which varies from 2485 by but 11 heat-units. 

Heat taken up by the water in the boiler per pound 0} coal as fired: 

II37.7 X 746457 =I0033B ,t.u. 
84643 



Heat radiated per pound of coal: 

I 4555- I °033- 2 485 = 2037 B.T.U. 



Heat carried off by flue gases: 
2485 X IO ° 
14555 



= 17. 1 per cent. 



Heat lost by radiation: 

2037 x 100 



14555 



= 14.0 per cent. 



BOILER-TESTING. 463 

Heat Balance. — The heat given up by the coal is accounted 
for as heat put into making steam, as heat carried off by the 
flue-gases, and as heat radiated from the setting to the air. 

The heat taken up in making steam and that carried off by 
the flue-gas may be calculated from the data obtained during the 
test, but the heat lost by radiation can only be found by subtract- 
ing the sum of the preceding from 100. This should be from 
8 to 15 per cent, depending on how hard the boiler is being forced, 
and on the amount and thickness of the brickwork. 

A Scotch boiler will show only 2 to 4 per cent loss by such 
radiation. 

Should the radiation come out negative it shows inaccuracy 
in the test. This inaccuracy may be due to errors in weighing 
coal or to the conditions at the start and at the end not being the 
same. At times, even though an engineer does his best to con- 
duct a test fairly, he may be cheated by the fireman. 

It is not out of place to point out here some of the ways by 
which an unfair result may be obtained by an honest engineer. 

1. By forcing the boiler abnormally for two or three hours 
before the test begins, thus storing up heat in the brickwork 
which is given out later when the boiler is under test. This may 
be obviated by keeping the boiler at its test rating for two hours 
before starting the test. 

2. If a boiler is working hard the water-level is lifted more 
than when the boiler is steaming easily. By crowding the boiler 
for a few minutes just as the test begins and by checking the 
boiler at the end of the test the indication by the glass may be 
made to vary one inch with the same amount of water in the boiler 
at the start and at the finish. 

As the level in the boiler is judged by the height in the glass, 
too much water would be put into the boiler near the end of the 
test when the rate of evaporation decreased. If the boiler is 
kept working at the same rate and at the same pressure through- 
out the test, the error from this source would be avoided. 

3. In many vertical boilers the water connection of the com- 



464 STEAM-BOILERS. 

bination carrying the gauge glass comes from the shell just above 
the crown-sheet. 

This makes a column of water outside the boiler perhaps 
10 feet in height. This column is balanced by the water inside 
the boiler. Just before beginning the test the fireman will blow 
out the combination (to satisfy you that it is working freely). 
The piping and glass now fill with hot water, and the level in the 
boiler and the level in the glass are the same. As there is no 
circulation in the pipe leading to the water end of the combina- 
tion, the water gradually cools and a column of cold, or com- 
paratively cold, water is balancing a column of hot water in the 
boiler. 

If the level in the glass is made the same at the end of the 
test as at the beginning, the level in the boiler will be from 6 
to 10 inches higher than at the beginning. By having the com- 
bination blown just before the end of the test this error is avoided. 

4. Sometimes plans to cheat the engineer are deliberately 
made. The engineer may insist that the blow-off pipe and all 
feed-pipes, excepting those from his weighing-tanks, be blanked, 
and yet he may get an impossible evaporation. 

A small pipe 1/4 inch in diameter starting below the water- 
line may lead up inside of the steam-pipe and run perhaps 100 
feet, where it appears on the outside of the pipe as a drip-pipe 
for removing condensation from the pipe. It is evident that if 
this " drip-valve" is manipulated most any evaporation could 
apparently be obtained. 

If an engineer has any doubts about the honesty of the parties 
concerned he may protect himself against any cheating similar 
to that referred to above by cutting the boiler under test from the 
steam-main and by blowing all the steam generated into the air 
through an orifice of known area. 

The weight of steam (figured by Rankine's or Napier's for- 
mula) flowing through the orifice plus the steam used in the 
calorimeter plus the steam used by the feed-pump should equal 
the feed-water weighed. 



BOILER-TESTING. 465 

Thermal Efficiency of a Boiler. — It has already been pointed 
out that the thermal efficiency of a boiler is the ratio of the heat 
utilized by the boiler from a pound of coal to the heat given up 
by a pound of coal. 

A thermal efficiency of 100 per cent would mean that there 
was no radiation from the brickwork setting, and that the flue 
gas left the boiler at the temperature of the room. 

It may be of interest to figure what efficiency might be ex- 
pected under the most favorable conditions. The amount of 
air needed to burn a pound of bituminous coal theoretically 
figures approximately 12 pounds, as will be seen by reference 
to Chapter III. 

The flue gases leaving a boiler which is working at capacity 
will be in the vicinity of 450 F., and if the temperature of the 
room be taken as 50 , the amount of heat per pound of coal 
carried off by the flue gas is 

12.85 X (450 - 5°) X 0.24 = 1234. 
The 12 pounds of air unites with 0.85 pound of carbon in the 
coal, making 12.85 pounds of flue gas. 

An average grade of soft coal gives up 14,650 B.T.U. per 
pound, and if the minimum radiation from the setting be taken 
as 5 per cent (it is more often 8 to 10), then the heat lost in this 
way is 0.05 X 14,650 = 733 B.T.U. 

1234 + 733 = 1967; 
14,650 - 1967 = 12,683; 
12,683 ^ J AfiS° = 0-865 or 86.5 per cent. 

Actually at least 18 pounds of air are required as a minimum 
per pound of coal, because it is impossible to distribute the 
theoretical amount in such a way that all parts of the fuel bed 
get the proper allowance. A similar calculation made with 
18.85 pounds of flue gas, instead of 12.85, an d with 5 per cent 
radiation, gives 82.7 per cent as a result which might be obtained. 

Some recent tests of long duration, made by Prof. D. S. 
Jacobus, an expert of the highest standing, on a boiler of large 



466 



STEAM-BOILERS. 



furnace capacity compared with the radiating surface of brick- 
work, Fig. 57, have shown efficiencies as high as 80 per cent. 
These tests were made with the boiler equipped with both the 
Roney and the Taylor stokers. The results were practically 
the same. The upper line in Fig. 224 shows the variation in 
efficiency as the capacity was increased. The lower lines give 
the per cent of steam used by the stokers. 



83 























































































































































































































































3 80 


























































u 

1 t 76 


















































































































































































































































£74 


























































































































72 
























































































































































































Sb D 5 


























































































































w 3 
-£ 3 


























Ta 


yi« 


r 












































































R 


HH 












O u 


























































Cm 























































































































70 90 110 130 150 170 190 210 

Per Cent of Rating on Basis of 10 Sq.Ft.of Boiler 
Heating Surface =1 Horse Power 

Fig. 224. 

Graphic Log Sheet. — Some of the ways by which an honest 
but inexperienced engineer may be tricked, have been noted 
under " Heat Balance." 

It is always advisable to carry along a graphic log sheet 
and fill this out hour by hour as the test progresses. Any ir- 
regularity in the water line, if not met by a corresponding 
irregularity in the coal line, at once gives warning that something 
is wrong. The log sheet at a glance shows whether or not 
conditions were stable during the test. Profile paper or the 
regular cross-section paper ruled to tenths may be used for this 
work. Fig. 225 shows such a log sheet. 




01 S 001 s 


5 t 2 3 I 

aaowrm 

J.UVHO 
3H0WS 


001 06 08 

aonwo 

•S3Bd 
WV319 


35 03 


81 9t tl 
SONHOd 0001 N 


31 OT 8 9 i 3 
NOIldWnSNOO 1VOO 




SS OS 


S* 0* S8 
sawnod oooi ni 


Ofi S3 03 St 01 S 

NOIldWnSNOO H3XVM 


009S 002S 0081 00H 0001 

*JoS3Hniva3dW3X 3fVH QNV 30VNUnd 


009 1 

! 


001 08 09 01- 03 
S3tjrUVU3dW31 H3XVM Q33J 

qnw woo« wsiioa 'saisina 



CHAPTER XIII. 

BOILER DESIGN. 

In order to bring together the principles and methods 
which have been given in the preceding chapters, they will be 
applied to the design of a boiler. Designing of any sort is an 
art that is guided and controlled by practical considerations 
and theoretical principles, and which can be acquired by prac- 
tice only. The design of a boiler, like many other designs, 
is further modified to meet the requirements of government 
boards of inspection, or to conform to the inspection-rules of 
insurance companies. These rules and requirements vary 
from place to place and from time to time; they must be 
known to the designer, but they have no place in a text-book. 
A simple and common type of boiler has been chosen for 
design ; the methods, with proper modification, can be applied 
to other types, and the general principles illustrated are much 
the same for all types. 

Type of Boiler. — The kind of boiler used in a given 
locality depends on custom, on the kind of water used, and on 
the cost and quality of fuel. Deviation from common prac- 
tice should be made only for sufficient reason. Where water 
is bad or where fuel is cheap, the plain cylindrical boiler or a 
flue-boiler will be chosen. With clean, soft water the cylin- 
drical tubular boiler, like that shown by Plate I, has been 
found to be convenient, economical, and cheap. All these 
boilers have external furnaces, so that the shell is in part 
exposed to the fire. Now plates exposed directly to the fire 
should not be more than half an inch thick; 3/8 of an inch is 
preferable. Though thicker plates are sometimes used, this 

468 



BOILER DESIGN. 469 

consideration limits the size of boilers of this type when high 
pressures are used. The importance of high efficiency for the 
longitudinal riveted joint becomes apparent in this connec- 
tion. 

Internally-fired boilers, like the Lancashire or the Scotch 
marine boiler, are not limited in diameter by this reason. 
The marine boiler sometimes has plates an inch and a quarter 
thick ; the fact that so great a thickness is undesirable some- 
times serves as a check on the size of such boilers. 

General Proportions. — Whatever may be the type of 
boiler chosen, there must be provided — 

1. Sufficient grate-area to burn the fuel required under the 
available draught. 

2. Suitable combustion-space to properly burn the fuel. 

3. Sufficient area of flues or tubes to carry off the products 
of combustion. 

4. Sufficient heating-surface to absorb the heat generated. 

5. Proper water-space to prevent too great a fluctuation 
of the water-level when there is an irregular demand for steam. 

6. Suitable steam-space to prevent too great a fluctuation 
of pressure when steam is taken at intervals, as for the cyl- 
inder of a steam-engine. 

7. Sufficient free-water area for disengagement of steam. 

The last three conditions are not fulfilled by most water- 
tube boilers; some such boilers depend on a separator for 
disengaging steam from water. 

Problem for Design. — Let it be required to determine 
the main dimensions and some of the details of a hori- 
zontal cylindrical tubular boiler to develop 80-horse power 
A. S. M. E. standard (page 218). Let the working-pressure 
be 150 pounds per square inch by the gauge, and the test- 
pressure 225 pounds, or once and a half the working-pressure. 

Assume that anthracite coal will be used, and that it will 
give an equivalent evaporation of 9 pounds of water per 
pound of coal from and at 212 F. Assume further that 12 



470 STEAM-BOILERS. 

pounds of coal will be burned per square foot of grate-surface 
per hour. 

The heating-surface may be about thirty-seven times the 
grate-surface. Tubes 16 feet long will be used, which length 
should not much exceed sixty times the diameter. 

The area through the tubes will be made about 1/7.5 °f 
the grate-area. 

Grate - area. — The A. S. M. E. standard requires that 
34.5 pounds of water per hour shall be evaporated from and 
at 212 F. for each horse - power. The total equivalent 
evaporation will consequently be 

80 X 34.5 = 2760 pounds per hour. 

With an equivalent evaporation of 9 pounds of water per 
pound of coal the coal burned will be 

2760 -r- 9 = 307 pounds per hour. 

With a rate of combustion of 12 pounds of coal per square 
foot of grate surface per hour, the grate-area must be 

307 -T- 12 =25.6 square feet. 

Tubes. — A common rule for finding the diameter of 
tubes is to allow one inch for each four feet of length when 
soft coal is used, and five feet when hard coal is used. A 
tube three inches in diameter will very nearly fulfil this 
condition. 

The table of proportions of flue-tubes in the Appendix, 
gives the area of the internal transverse section of such a tube 
as 6.08 square inches; the external area is 7.07 square inches. 
The internal circumference is 8.74 inches, and the external 
circumference is 9.42 inches. 



BOILER DESIGN. 47 1 

The aiea through the tubes has been chosen as 1/7.5 of 
the grate-area, equal to 

25.6 X 144 . , 
= 492 square inches. 

Since the area through one tube is 6.08 square inches, 
there will be required 

492 -7-6.08 = 80.8, 

or, more properly, 81 tubes. It may be found convenient in 
laying out the tube-sheet to use more than this number of 
tubes; a less number is of course improper. 

Steam-space. — A good rule for this type of boiler is to 
allow from 0.8 to 1 cubic foot of steam-space per horse- 
power, which gives from 64 to 80 cubic feet for this boiler. 
We will assume 80 cubic feet. 

For sake of comparison, calculations will be made also by 
rules given on page 216. Thus for certain boilers working at 
moderate pressures it is found that the steam-space may be 
made equal to the volume of steam used by the engine in 20 
seconds. Suppose that this boiler, though designed for 150 
pounds pressure, may run at 70 pounds pressure, and may 
supply an 80 horse-power engine which uses 30 pounds of 
steam per horse-power per hour. 

Now the volume of one pound of steam at 70 pounds by 
the gauge, or 85 pounds absolute, is 5.16 cubic feet. So 
that the engine will use 

80X30X5.16=12,384 

cubic feet of steam in an hour, or 

20 

-7— X 12384=68 
3600 ° 

cubic feet in 20 seconds. This is about the lower limit by 
the rule used above. It is clear that the steam-space would 



472 STEAM-BOILERS. 

be very small if determined by this rule for an engine using 
steam at 150 pounds pressure. 

Another rule makes the steam-space from 50 to 140 times 
the volume of the high-pressure cylinder of the engine; 50 
for very high pressure and high speed, 140 for slow speed 
and low pressure. For medium speeds and pressures 60 to 
90 may be used. 

The boiler under consideration may supply steam to a 
triple-expansion engine which has a high-pressure cylinder 9 
inches in diameter by 30 inches stroke, so that the volume is 
1. 105 cubic feet. According to this the steam-space needed 
is 66 to 99 cubic feet. 

Diameter of Boiler. — For this type of boiler the steam- 
space is commonly made one third and the water-space two 
thirds of the contents of the boiler. To the contents of the 
boiler there must be added the space occupied by the tubes to 
find the volume of the cylindrical shell. Now we have de- 
cided to use 81 tubes 3 inches in diameter and 16 feet long. 
The area of the external transverse section has been found to 
be 7.07 square inches. The space occupied by the tubes is 
consequently 

81 X 7-07 X 16 



144 



= 64 cubic feet. 



To this add steam-space, 80 

and water-space, 160 



Making in all, 304 " " 

The cylinder is 16 feet long, so that its transverse area is 

304 -h 16 = 19 square feet; 

which corresponds to a diameter of 59.02 inches, or nearly 60 
inches. This will be taken as the trial diameter; it may re- 
quire change in proportioning other parts of the boiler. 

The method of determining the main dimensions of a 



BOILER DESIGN. 473 

boiler from the steam-space will require modification if it is 
applied to any other type of boiler. Even when applied to 
a given type it leaves much to the judgment of the designer, 
who may find difficulty in using it unless he is accustomed to 
working on that particular type. If the designer has at hand 
the dimension of several boilers of a given type, he may pre- 
fer to select the main dimensions for a new design directly, 
with the reservation that such dimensions may be modified 
as the design proceeds. This is commonly done by the 
designers of marine and locomotive boilers. 

Heating-surface. — The heating-surface of a cylindrical 
tubular boiler consists of all the shell below the supports at 
the side wall, all the inside of the tubes, and part of the rear 
tube-plate. Usually half of the cylindrical part of the shell 
is heating-surface. In the case in hand the heating-surface, 
exclusive of the tube-pfate, will amount to 

cu 11 l w 3.I4I6 X 60 X 16 

Shell - X = 125.7 sq. ft. 

_ t o 8.74 X 16 

Tubes.... 81 X — — = 943.9 " " 



Total 1069.6 " " 

The grate-surface is to be 25.6 square feet, so that the 
ratio of grate-surface to heating-surface will be at least as good 
as 

25.6 : 1069.6 :: 1 : 41J. 

The actual ratio will be more favorable as it will appear 
advisable to use more than 81 tubes, and the back tube-sheet 
remains to be allowed for. 

Water-level. — It is now necessary to determine the posi- 
tion of the water-level to see if there will be sufficient free- 
water surface and sufficient distance from the water-level to 
the shell above it. 



474 STEAM-BOILERS. 

Since the whole boiler is cylindrical, the area of the head 
of the boiler exposed to steam and to water will have the 
same ratio as that of the steam-space to the water-space. 
Consequently the area of the head above the water-level must 
be one third of the total area of the head less the combined 
areas of the tubes. 

The area of a circle having a diameter of 60 inches is 
2827.4 square inches. The area of 81 tubes each having an 
external cross-section of 7.07 square inches will be 

81 x 7-07 = 572.7 

square inches. The area of the head exposed to steam is 
consequently 

2827.4- 572 .7 = ;s j 6 
3 

square inches. We need now to know the height of a seg- 
ment of a 60-inch circle, which has the area of 751.6 square 
inches. The second problem in the explanation of the use of 
a table of segments (see Appendix) gives for the tabular 
number corresponding to the area 

751.6 

0.2088; 



60 X 60 

for which the ratio of the height to the diameter is 0.312. 
The height of the segment is therefore 

0.312 X 60 = 18.7 inches. 

This gives sufficient height above the water, and sufficient 
free-water surface. The water-level will be 

30 - 18.7 = 11. 3 

inches above the centre of the boiler. 

Factor of Safety. — It has been pointed out that the actual 
factor of safety of boiler-shells is usually four or five when the 
boiler is built. The apparent factor of safety for some parts 



BOILER DESIGN. 475 

like stay-bolts may be greater, but such factors are illusory 
because the stays may be subjected to considerable irregular 
stress from unequal expansion. The apparent stress on stay- 
rods and bolts, from steam-pressure only, is frequently limited 
by inspection-rules or by law. 

The factor of safety of a boiler which has been at work 
for some years is much affected by corrosion, which acts upon 
different parts of the boiler very differently, even when the 
corrosion is uniform. Thus a plate half an inch thick will 
have 7/8 of its original strength after it has lost 1/16 of an 
inch by corrosion. The weakest part of the plate, that is, 
the riveted joint, seldom suffers as much from corrosion as the 
whole plate at a distance from the joint, because the plate is 
protected to some extent by the rivet-heads. Some forms of 
joint have an internal cover-plate, which protects the plate at 
the joint and the joint may be nearly as strong after corrosion 
as before. Very often old weak boilers fail by tearing the 
corroded plate outside the riveted joint. 

Stay-rods and bolts suffer much more from corrosion than 
plates. Thus a rod one inch in diameter has an area of 
0.7854 of a square inch. After corrosion to the extent of 
1/16 of an inch has taken place the diameter is 7/8 of an 
inch and the area is 0.6013, which is 

0.6013 -^ 0.7854 = 0.766 

ot the original area. Compare this with the plate which 
retains 7/8 or 0.875 oi i ts thickness after the same amount of 
corrosion. Of course a smaller stay will suffer more, and a 
larger one less, in proportion. 

After the sizes of the parts of a boiler are decided upon it 
is well to make calculation to see that a factor of safety of 
four will remain after a reasonable amount of corrosion. Or, 
as in the case of stay-rods, the size may be calculated with a 
proper factor, and then the diameter may be increased to 
allow for corrosion. 



476 STEAM-BOILERS. 

Thickness of Shell. — The final decision of the proper 
thickness of the shell for the boiler under consideration can- 
not be made until the efficiency of the joint is known; but 
the efficiency of any of the complex joints now in vogue can 
be found only when the thickness of the plate is known. It 
is therefore convenient to assume a factor of safety of about six 
and make a preliminary calculation. 

Thus for the boiler in hand w r e will get for the thickness 



t= 150x30 

55,000 ~ 6 * 

of an inch. A similar calculation with a factor of five gives 

150 X 30 _ n f7 

t — = 0.4.1 

55,000-- 5 

of an inch. The shell will be either 7/16 or 1/2 an inch 
thick. Seven sixteenths will give an apparent factor of 
safety of 

55 ,000 x 7/ig = ., 

150 X 30 " 

After the allowance for the efficiency of the joint has been 
made this factor will be found to be about 4f . 

Longitudinal Joint. — The shell-plate is made as thin as 
possible because it will be exposed to the fire. Consequently 
the efficiency of the longitudinal riveted joint must be high if 
the real factor of safety is to be satisfactory. The strength 
of triple-riveted joints like that shown on page 284 ranges 
from 85 to 90 per cent. The joint with two cover-plates 
shown by Fig. 226, will be chosen. Following the method 
given on page 284, it appears that this joint may fail in one 
of five ways, for which the resistances are as follows: 

A. Tearing at outer row of rivets: 

Resistance = (P — d)tft. 



BOILER DESIGN. 



477 



B. Shearing four rivets in double shear and one in single 

shear: 

_ . Qitd' 1 „ 

Resistance = /,. 

4 

C. Tearing at the middle row of rivets and shearing one rivet: 

Resistance = (P — 2d)tf t -\ f s . 




4 J/ > 



r^ 



( ;) 



(( 1 



Fig. 226. 

D. Crushing four rivets and shearing one: 

nd? 
Resistance = ^dtf c -\ f s . 

E. Crushing five rivets: 

Resistance = Adtf c + dt c f c . 

The diameter of rivet will be found by equating the 
resistances A and C. 

7td* 

. , Aift 4 X tVX 55. QQQ : q 

. . a = —7- = = 0.00. 

n f s ^45,000 



478 STEAM-BOILERS. 

The rivet which was used was 1 3/1 6 of an inch when driven. 

There are several methods in which we may find the way 
in which the joint will fail, and then find therefrom the effi- 
ciency. One is that shown on page 285 by assuming a pitch 
and calculating the resistance of the joint to failure in each 
of the five several ways. Another method is to equate the 
five several resistances two and two and calculate the pitch; 
the least pitch thus found must not be exceeded. Thus 

Equating B and C, 

A = {P _ 2d)tfi +*Al u 

4 4 

At ft 



8 X 3.Hi6x(^|) 



4X i6 



45,000 , 13 

X — + 2 X -1= 9- 

7 55,ooo r 16 



Equating A and B, 



■■■ p = 9 -£i+< 



9X3.Hi6(l|) J 



45,000 L 3 

7 55,000 * 16 

4X F6 



Equating A and D, 



4 



BOILER DESIGN. 479 

ft At ft 

3.14.6 x(^V 
13 95,000 _ m6^ 4^000 £3 

~ 4 X i~6 X 55^55 + " A y 7 " X 5 5,ooo + .6 - 7 ' 4 " 

Equating A and E, 

(P-d)tf t = 4 dtf c + <it c f c . 

ft l ft 

-a v I 3 n/ 95>QQQ , 13/16 X 3/8 Qj^ooo 13 __ 
" 4X 16 X 55,000 + 7/16 ~ X 55,000+16 h * 

Here t the thickness of the cover-plate, is taken to be 3/8 
of an inch. 

The greatest allowable pitch at the outer row of rivets is 
evidently 7.4 inches. 

Instead of going to the labor of solving all four of the 
above equations, we may find by some other method how the 
joint is likely to fail, and make up an equation involving 
those resistances only. Thus a rivet in the outer row may 
fail by shearing or by crushing at the cover-plate, which is 
here made thinner than the shell-plate. Equating the re- 
sistances of the two methods, we have 

4 
or for a cover-plate 3/8 of an inch thick 

d = AXi 95^oo =iQi 

7t 45,000 

A rivet 1.01 inch in diameter wiil consequently be just as 



480 STEAM-BOILERS. 

likely to fail by crushing as by shearing. But the resistance 
to shearing increases as the square of the diameter, while the 
resistance to crushing increases as the diameter. It is there- 
fore evident that a rivet larger than i.oi of an inch will fail by 
crushing, while a smaller rivet will fail by shearing. 

A similar calculation at the inner row, when the rivet 
bears against a cover-plate both inside and outside, and will 
consequently crush against the shell-plate, gives 

——f s = tdf c ; 
^ = lXA x ?5^oo = o6- 

7t 45,000 

Here a rivet larger than 0.6 will crush, and one smaller 
will shear. It is now evident that a 13/16 rivet will shear 
at the outer row and will crush at the inner row. That is, for 
this joint the failure will occur by the method D, but not by 
the methods B or E. Then equating the resistances A and D, 
and solving for P y we get for the pitch at the outer row 7.4 
inches as before. The corresponding pitch at the calking 
edge of the outer cover-plate is 3.7 inches; we will choose for 
that pitch 3-jj- inches, making the pitch at the outer row 7J 
inches. 

The efficiency of the joint is 

ioo ^"" d = 100 X ^~^ = 88.8 per cent. 

In the preceding article the apparent factor of safety 
based on the whole strength of the shell-plate is 5,35. Al- 
lowing for the efficiency of the longitudinal joint, the real 
factor of safety when the boiler is new is 

0.888 X 5-35 =4.75. 



BOILER DESIGN. 481 

With this style of joint the shell-plate is protected from 
corrosion by the inner cover-plate, and the joint will lose 
little if any efficiency from corrosion. If it be assumed that 
the plate loses 1/16 of an inch by corrosion during the life 
of the boiler, then the strength of the plate will be one 
seventh less after corrosion, and the corresponding factor of 
safety will be 

5-35 X f = 4-6, 

which may be considered to be sufficient. 

Ring-seam — The stress on a transverse section of a 
homogeneous hollow cylinder from internal fluid pressure is 
one half the stress on a longitudinal section. It will in gen- 
eral be found that a single- or a double-riveted ring-seam is 
sufficient for any cylindrical boiler-shell. Marine boilers 
commonly have double-riveted ring-seams; externally-fired 
horizontal boilers seldom have the shell more than half an 
inch thick, and for that thickness, or less, single-riveted ring- 
seams are used. 

It is found in practice that ring-seams of horizontal ex- 
ternally-fired boilers may have a pitch of about 2 T \ inches for 
all thicknesses of plate from 1/4 to 1/2 of an inch. The 
diameters of rivets for such seams may be made about the 
size given in the following table : 

Thickness of plate £ -fa f T 7 ¥ J 

Diameter of rivet i \i i i $ 

The ring-seam in question has a circumference of about 

3.1416 X 60 = 188.2 

inches, which will allow us to use 84 rivets with a pitch of 
about 2.24 inches. This joint will fail by shearing the rivets. 
The efficiency of the joint is consequently the ratio of the 
resistance of a single rivet to shearing, to the resistance of 



482 STEAM-BOILERS. 

a strip of plate as wide as the pitch. Consequently the 
efficiency is 

nd* 

4 fs = i X 3-i4i6 X (H) 2 X 45.QQO = 

ptf t 2.24 x -iV x 55,000 * 433, 

which is more than half of the efficiency of the longitudinal 
seam, and will consequently be sufficient. 

Lap. — The lap, or distance from the centre of the rivet to 
the edge of the plate, is usually taken as 1.5 times the diam- 
eter of the rivet used, which makes the distance of the edge 
of the hole from the edge of the plate equal to the diameter 
of the rivet. For the single-riveted ring-seam this makes the 
lap equal to 

1-5 XH= 1-22. 

It is customary to calculate the width of lap required on 
the assumption that the metal between the rivet and the edge 
of the plate may be treated as a beam of uniform depth, fixed 
at the ends and loaded at the centre by the force which would 
be required to shear or crush the rivet, taking, of course, the 
larger. The width of the beam is the thickness of the plate, 
the depth is the distance from the edge of the hole to the 
edge of the plate, and the length is the diameter of the rivet. 

Rivets in single-riveted seams fail by shearing. The load 
is consequently the shearing resistance 

7td* 

The maximum bending moment for a beam of uniform 
section fixed at the ends and uniformly loaded is equal to 
the load multiplied by one eighth of the span. The moment 
of resistance is equal to 

A 



BOILER DESIGN 483 

in which /is the cross-breaking strength (about 55,000), /is 
the moment of inertia of the section, and y is the distance of 
the most strained fibre from the neutral axis. Here we have 

T th 2 h 

12 2 

representing the distance from the edge of the hole to the 
edge of the plate by h. 

Equating the bending moment to the moment of re- 
sistance, 

4 o 






3 x 3-1416 x 13 45,ooo 

X z = 0.77 

' f r r\r\r\ ' ' 



6xlx.6 ! 55 ' 00 ° 

ID 

for the case in hand. The lap is consequently 
Q-77+1 X J| = i.i8 

2 ID 

inches for the ring-seam, which is somewhat less than that by 
the arbitrary rule that it should be once and a half the diam- 
eter. 

A similar calculation for the cover-plates with the same 
diameter of rivet, but with a plate 3/8 of an inch thick, gives 
for the lap 1.24 or i-|- of an inch, while the arbitrary rule gives 
1.03 of an inch. It is probable that the lap may be consider- 
ably smaller than is given by the calculation by the beam 
theory, but for lack of direct experimental knowledge on this 
question it is not wise to make the lap much less than the 
calculation gives; we will consequently use ij of an inch for 
the lap of the cover-plates. 



484 STEAM-BOILERS. 

The rivets of the inner rows pass through both cover-plates 
and are in double shear, and consequently fail by crushing 
as is shown on page 480. The load to be used for calculating 
the lap is therefore the resistance to crushing in front of the 
rivet ; that is, we here have for the load tdf c . The equation 
of bending moment and moment of resistance gives 

1 tti 

-dxtdf c =f—. 



v/g-iVJ^s?- 



4 X 45>°°o 
The lap is consequently 

0.926 + ^ X y 6 = 1.27, 

or a little more than ij. The lap used is if of an inch. 

Tube-sheet. — The next step in the design is to lay out 
the tube-sheet on the drawing-board. If possible, the tubes 
should be arranged in horizontal and vertical rows as shown 
on Plate I. The distance between the tubes should not be 
less than three fourths of one inch ; one inch is better. On 
Plate I the horizontal rows are spaced one inch apart, while 
the vertical rows are only three fourths of an inch apart ; wider 
spacing for horizontal rows is more favorable for the free cir- 
culation of water and the disengagement of steam. The cir- 
culation is improved by having a space in the middle as shown 
on Plate I 

If a very large number of tubes are required for a given 
boiler, they may be arranged in vertical rows and in rows at 
30 with the horizon, as on Plate II. This arrangement is 
commonly used for locomotive boilers, but is not favored for 
stationary boilers. 

The common range of fluctuation allowed for the water- 



BOILER DESIGN. 485 

line with this type of boilers is six inches, three above and 
three below the mean water-level. The tops of the tubes are 
set about three inches below low water-level. 

The tubes should nowhere be nearer than three inches 
from the shell, and the bottom row should be from four to six 
inches from the bottom of the boiler. 

The hand-hole near the bottom of the head should be 
placed as low as possible; the flat surface for the gasket should 
be at least 3/4 of an inch wide. No tube should be nearer 
than an inch from its edge. 

The tube plate is usually from 1/16 to 1,8 of an inch 
thicker than the shell-plating. The internal radius of the 
flange should not be less than half an inch. For plates half 
an inch thick or less the outside radius is commonly made one 
inch. 

In applying these principles to the tube-sheet for a boiler 
60 inches in diameter, as shown on Plate I, it appears that 84 
tubes may be used, spaced four inches horizontally and 3J 
vertically and with a space at the middle for circulation, pro- 
vided that the top of the upper row of tubes is 6\ inches 
above the centre-line of the boiler. This brings the water- 
level 

6i+6= 12 i 

inches above the middle of the boiler, instead of 11. 3 as caL 
culated on page 474; that is, the water-level is raised 1.2 of 
an inch or 1/10 of a foot. At 12 inches above the middle, 
the boiler is about 4-J feet wide; the layer of water added has 
consequently a volume of 

1/10 X 4-5 X 16 = 7.2 

cubic feet. The effect is to reduce the steam-space from 80 
cubic feet (see page 471) to 72.8 cubic feet. But the rule 
used gave from 64 to 80 cubic feet, so that 72.8 cubic feet is 
a fair allowance. If the tubes were spaced nearer together 
in the horizontal rows and the space for circulation were 



4 86 



STEAM-BOILERS. 



omitted, the required number of tubes could be easily provided for 
without raising the water-level. If in any case a satisfactory ar- 
rangement of tubes cannot be made with the diameter assumed 




from preliminary calculations of steam- and water-space, or from 
some other method, then a larger diameter must be used. 

If a manhole is put in the front head the tube-sheet is as 
shown in Fig. 227. There are now 74 tubes instead of 84, and 



BOILER DESIGN. 487 

the heating-surface is reduced by 116.5 square feet, leaving a 
total of 978.8 square feet, or about 12.5 square feet to a horse- 
power. The head under the tubes is stayed by angle irons tied 
to the head by two through rods. This staying is figured in the 
same manner as the channel-bars, which are considered later in 
this chapter. 

Area of Uptake. — The area of the uptake, like the total 
area through the tubes, is made from 1/7 to 1/8 of the grate 
area. On page 471 the area through the tubes was found to 
be 492 square inches. The uptake may be made 12 inches 
deep, measured from front to rear. It will then be 

492 ~ 12 =41 

inches wide, measured transversely. The opening through 
the top of the projecting shell at the front end will be made 
12 inches deep, as shown on Plate I, and must be cut down 
till it is 41 inches wide. The projecting end of the shell is 
made long enough so that a space of about one inch is left 
between the uptake and the calking edge of the front tube- 
sheet. 

Length of Sections. — The length of the rings or sections 
of the cylindrical shell is limited by the reach of the riveting- 
machine and by the width of plate obtainable. The sec- 
tions are often made the same length, though there is no other 
reason for this than the convenience in ordering material. 
The two rear sections on Plate I are each made 68 inches from 
centre to centre of riveted joints, or, allowing ij- of an inch 
for lap at each end, the plates when finished are 70 J inches 
wide The front section is 

14+ 54f + ii = 6 9 % 

inches wide. In this case the plates could all be ordered 
about 72 inches wide. 

The front course which comes over the fire is an outside 
course, so that the flames may not strike directly against the 



488 S TEA M-BOILERS. 

edge of the plate at the ring-seam. The length of the grate 
is commonly about one third of the length of the boiler, 
which brings the first ring-seam over the bridge, where the fire 
is the hottest. It is well to avoid this by making the front 
section shorter, and the other sections longer. 

Manholes, Hand-holes, and Nozzles.- — These fittings 
should be strong enough and stiff enough to carry the stresses 
which come from the direct steam-pressure and from the ten- 
sion in the pieces to which they are fastened ; for example, 
the manhole-ring must be able to take the place of the piece 
of plate cut away at the hole. 

All these fittings can now be bought in the form of steel 
forgings, made by a hydraulic flanging or forging machine. 
Gun-iron and cast steelare, however, much used. 

The determination of stresses in a manhole-ring, even if 
approximate methods are used, is both difficult and uncertain, 
and will not be considered here. Forms and dimensions that 
have been used in good practice may be taken for a guide in 
designing. A rule used by boiler-makers for forged rings, 
which, like that shown on Plate I, lie close to the shell-plate, 
is to make the section of the ring, exclusive of the lip, equal 
at least to the section of the plate cut away. The aid given 
by the lip against which the cover bears is considered to 
offset eccentric loading, etc. The ring of a steam-nozzle may 
be treated in the same way, though it is more efficiently aided 
by the cylindrical portion. Gun-iron manhole-rings should 
be \\ of an inch thick, and nozzles may be \\ of an inch thick. 

An approximate calculation of the stress in the manhole- 
cover may be made by treating it as a beam supported at the 
ends and loaded by the steam-pressure and by the pull of the 
bolt at the middle; this last must be assumed, as it cannot be 
known. The calculated stress will be in excess of the actual 
stress, since the plate is supported all around. The handhole- 
plate may be treated in a similar way. Handhole-covers are 
frequently drawn up by a taper key instead of a bolt and nut, 



BOILER DESIGN. 



489 



because the nut is exposed to the fire, and often cannot be 
removed with a wrench, after it has been in place some time. 

The bearing-surfaces of the manhole-cover and the lip 
against which it bears should be machined to make them 
true and smooth, though this is not always done. The hand- 
hole-cover may be finished, but it bears directly against the 
plate, which of course is not finished. In any case the joint 
is made tight by a gasket which may be 3/4 of an inch wide 
for the hand-hole and from that width to an inch for the man- 
hole. 

Staying", — As is pointed out on page 312, the calculation 
of stresses in a flat plate supported at intervals can be 
determined only by the application of the theory of elasticity; 
and the only determinate case is that in which the supported 
points are in equidistant rectangular rows, dividing the sur- 
face into squares. This case applies directly to the staying 
of the fire-box of a locomotive by stay-bolts. Whatever 
system of arranging the supported points is finally chosen, it 
is convenient to make a calculation for the determinate case, 
with the points in equidistant rows, in order to get a standard 
with which the chosen system may be compared. 

The equation for finding the stress in a flat plate supported 
at points in equidistant rectangular rows is 

in which a is the distance of points in a row, / is the thickness 
of the plate, and p is the steam-pressure in pounds per square 
inch. In the design in hand t = 9/16 of an inch and p = 
150 pounds. Assuming 

/=tV X 55,ooo= 5500, 
and solving for a, we have 

IVJ? / 9X 5500 X 9"X~9 „ , • t, 

^ = V2"7 :== V2Xi50Xi6xi6 :=7 + mches - 



4QO S TEA M-B OILERS. 

If the distance between supported points is made less than 
7 inches, whatever the system of arrangement may be, we 
may be confident that the stresses will not exceed 5500 
pounds; in this case stresses in the plate are due only to the 
pressure on the plate, since the shell of the boiler is self-sup- 
porting. 

In the several ways of staying the flat ends of boilers 
shown on pages 225 to 229 the plate is riveted to channel- 
bars, angle-irons, or crowfeet, which in turn are supported by 
stay-rods. The rivets are in direct tension, and are subject to 
initial stresses due to the contraction when they cool; it is 
customary to limit the apparent working stress to 6000 
pounds. Rivets less than 3/4 of an inch are seldom used, 
since in practice they are found to be too much affected by 
initial stress due to cooling. Large rivets are also considered 
to be undesirable. We will choose here 13/16 for the rivets. 

If each rivet sustains the pressure on a square a inches 
wide, then the stress per square inch on the rivet will be 

~rf s = 150 X a\ 

4 

in which d is the diameter and f s is the tensional stress. 
Assuming f s = 6000 and d = 13/16, and solving for a x , we 
have 



a ^\l 



n x 13 X 13 X 6000 

— 4.55 inches. 



150 X 16 X 16 



This gives for the limiting distance of rivets 4.55 inches. 
Of course a less distance may be used if convenient. 

In some cases the pitch of the rivets may be controlled by 
the system of staying. For example, the rods used with 
crowfeet are seldom more than \\ of an inch in diameter, 
because larger rods may bring too large a local stress where 
they are riveted to the cylindrical shell. Rods one inch or 
*m inch and an eighth are frequently used. A double crow- 



BOILER DESIGN. 49 1 

foot has four rivets, each of which will carry one fourth of the 
load on the stay-rod. A stay-rod \\ inches in diameter, 
and limited to a stress of 7500 pounds, may carry a pull in 
the direction of its length ot 

7500 X = 9204 pounds. 

If the rod makes an angle of 20 with the shell-plate, the pull 
which it will exert perpendicular to the head will be 

9204 cos 20 = 9204 X 0.93969 = 8649 

pounds, so that each rivet will carry about 2162 pounds. If 
each rivet supports a square having the side # a exposed to the 
pressure of steam at 150 pounds, then 

2162 = 150 X af, 



or 



/2162 n . „ 

= v t& = 3 in 



Laying out Stays. — Having selected the form of staying 
to be used, the plan must be laid out on the drawing-board, 
giving proper attention to practical considerations, such as 
the way in which the stays are to be inserted, and taking care 
that accessibility is not too much interfered with. Fig. 228 
repeats the upper part of the head of the boiler shown by 
Plate I, with certain additional dotted lines, which will be 
referred to in the explanation of calculations. The area to 
be stayed is considered to be limited by the upper row of 
tubes, and by a dotted line drawn i\ of an inch from the 
inside of the shelL This line is drawn at the right only; it is 
very nearly the place where the rounded corner of the flange 
joins the flat surface of the head. The distance of the lowest 
row of rivets from the top row of tubes, and of the outer row 
of rivets from the dotted line, may be as great as their maxi- 
mum distance from each other. Rivets should not be placed 
nearer than 3 inches from the tubes, lest the expansion of the 



49 2 S TEA M-B OILERS. 

tubes should start leaks. Rivets may be placed near the 
dotted line, if that is convenient. For example, the outer- 
most row of rivets in crowfoot staying (Fig. ,85, page 227) 
may be at a distance a^ from the dotted line; for \\ inch stay- 
rods <z 2 = 3.8 inches. 

The method of staying selected consists of channel-bars 
riveted to the head and supported by through-stays; the 
upper channel-bar is assisted by an angle-iron. The channel- 
bars selected are six inches wide, and the horizontal rows of 
rivets in each bar are 3J inches apart, which brings them as 
near the flanges of the bar as they can be driven. The mid- 
dle of the lower channel-bar is 5$ inches above the top of the 
tubes, so that the lowest row of rivets is 

5* ~ * X 3i = 4 

inches above the top row of tubes. • But the plate cannot be 
properly considered to be rigidly supported at a line drawn 
through the tops of the tubes; we will assume the line of 
support to be a fourth of the diameter lower down. This 
makes a space of 4f inches, instead of the 4.55 inches calcu- 
lated for 13/16 rivets. The excess may be considered to be 
offset by the fact that the other row of rivets in the channel- 
bar is only 3J inches distant. 

The upper channel-bar is placed 8 inches above the lower 
one, so that the stay-rods are 

30-(6i+5f+8) = 9i 

inches below the shell. If these upper rods are much less 
than 10 inches from the shell access to the boiler will be diffi- 
cult. The space immediately above the upper channel-bar is 
stayed by aid of an angle-iron which is riveted to the channel- 
bar. 

The distance of the lower row of rivets in the upper chan- 
nel-bar, above the upper row in the lower bar, is 

8 - l\ = 4f 



BOILER DESIGN. 



493 



inches — the same as the distance assigned to the lowest row 
of rivets above the assumed line of support at the top row of 
tubes. The top row of rivets in the angle-iron is only a 
little more than four inches below the dotted boundary-line. 

Lower Stay-rods. — In order to determine the load carried 
by the lower stay-rods, we will assume that half the load on 
the plate between the lowest row of rivets and the top row of 
tubes is carried by the rivets, and that the load on the plate 
between the channel-bars is divided equally between them. 
Now we have assumed that the line of support at the tubes is 
a quarter of their diameter below their tops, and have found 
this line to be 4f inches below the lowest row of rivets. Half 
of 4f is 2-f. Again, the distance between the top row of rivets 
in the lower channel-bar and the bottom row in the upper 
bar is 4f inches, of which half is 2§. The distance apart of 
the two rows of rivets in the channel-bar is 3^ inches. The 
total width of plate supported by the channel-bar may there- 
fore be considered to be 

2 f + 3i + 2| = 8 inches. 

The length of the lower channel-bar at the middle is 52 
inches, as measured on Fig. 228; but it is convenient to space 
the rods 13^ inches apart, and to consider the bar to have four 
equal spaces, which leads to an assumed length of 54 inches. 

The load on the lower channel-bar is considered to be 

150 X 8 X 54 = 64,800 pounds. 

We will treat the channel-bar as a continuous girder with 
four equal spaces and five points of support, of which three 
are at the stay-rods and two are at the shell of the boiler. 
By the theory of continuous girders a uniform load on the 
channel-bar would be distributed among the five points of 
supports as follows: At each point of support at the shell 
11/112, at each outer stay-rod 32/1 12, at the middle stay-rod 
26/112. This would bring on each of the outer stay-rods 
r \\ X 64,800= 18,514 



494 S TEA M-B OILERS. 

Now the load is not uniformly distributed, but is carried in 
part by the rivets and in part by the nuts and thick washers 
on the stay-rods; but the actual distribution will bring a less 
load on the two outer stays, so that the assumption of the 
load just found is on the side of safety, and it is conveniently 
calculated. 

If we assume 9000 pounds for the working-stress in the 
stay-rods, we may calculate the diameter by the equation 

nd" 1 _ 18,510 
4 9000 

which gives for the diameter something less than if of an 
inch. For simplicity all five stay-rods will be the same size, 
namely, 1} of an inch — that required for the two upper stay- 
rods. This is the diameter of the body of the rod ; the ends 
are enlarged to 2\ inches where the thread is cut for the nut. 

Lower Channel-bar. — The determination of the actual 
stresses in the channel-bar, allowing for the effect of the nuts 
and thick washers on the stay-rods, is very uncertain. On the 
other hand, the application of the theory of continuous girders 
with a uniform load may not give us a stress as large as the 
actual maximum stress. We will therefore use an approxi- 
mate method, which will give a stress at least as great as the 
greatest stress in the bar. 

For this purpose we will assume that a piece of the 
channel-bar cut by the lines ab and cd (Fig. 228) may be 
treated as a simple beam. These lines ab and cd are drawn 
at one fourth of the diameter of the thick washers from the 
centre of the rod, or at 

of an inch. We will further assume that the load on the pair 
of rivets A and B is due to the pressure of the steam on the 
area cfgh, bounded by lines drawn half-way between them 
and the nearest point of support. Thus eg is half-way 
between the rivets and the line ab, gh is half-way between the 



BOILER DESIGN. 



495 




4-*- 



496 STEAM-BOILERS. 

rivets and the line of support at the upper row of tubes, ef 
is half-way between the channel-bars, and fh is half-way to 
the next pair of rivets. The rivets are 4J- inches from the 
nearest stay-rod, and are 

41— if = 3t 

inches from the line ab\ half of this is i^J- of an inch. The 
two pairs of rivets are 

(13* -2 X4{) = 4 
inches apart ; half of this is 2 inches. The area of efgh is 

OH + 2) x s = 2 9 i 

square inches; and the steam-pressure on that area is 

29 J X 150 = 4425 pounds. 

This is the load due to each pair of rivets between a pair 
of stay-rods; and since the rivets are symmetrically placed, 
this is also the supporting force at each end of the beam. 
Between the two pairs of rivets the beam is subjected to a 
uniform bending moment, equal to the load on a pair of rivets 
multiplied by their distance from the end of the beam; that 
is, the bending moment is 

4425 X 3l= J 4934. 
The theory of beams gives 

y 

in which M is the bending moment, / is the moment of inertia 
of the section of the beam, y is the distance of the most 
strained fibre from the neutral axis, and / is the stress at that 
fibre. For rolled-steel channel-bars we may use, for/, 16,000 
pounds, so that with the given value of M we have 

16,000/ / 

14,934 = — , or - = 0.933. 



BOILER DESIGN. 497 

Now / and y depend on the form and size of the section 
of the beam, and, conversely, the size and form of beam 
required may be determined from them. But as the upper 
channel-bar is exposed to a greater bending moment and con- 
sequently must have a larger section than is required for the 
lower bar, we will defer the discussion of this matter, because 
it is convenient to make the bars of the same size. 

Upper Stay-rods. — The flat surface of the boiler-head 
above the lower channel-bar is supported by the upper 
channel-bar aided by the angle-iron which is firmly riveted to 
it, and which will be assumed to act with and form a part of 
the channel-bar. 

Following our general convention that the pressure on a 
portion of the head between two lines of support is divided 
equally between them, we will assume that the load on the 
upper channel-bar is due to the steam-pressure on an area 
bounded at the bottom by a line half-way between the upper 
and lower channel-bars, and at the top by an arc 3J inches 
inside the boiler-shell. On Fig. 228 half of this area is rep- 
resented by jkl\ the axcjk being about half-way between the 
root of the flange, shown by the outer dotted boundary line, 
and the adjacent rivets. In place of the area jkl we will take 
the rectangular area hnno, bounded at the end by a line at the 
middle of the end of the channel-bar, and at the top by a line 
mn so chosen as to make the rectangular area larger than the 
area it replaces. The width of this area, ////, is 9^ inches, so 
that the load per inch of length is 

9J- X 150 = I387-5 pounds. 

The upper channel-bar may be assimilated to a continuous 
girder with three unequal spans; the middle span between 
the stay-rods is 15^ inches, and the end spans between the 
stay-rods and the roots of the flange of the head are each 
1 1 J- inches. This makes the end spans nearly 3/4 of the 
middle span. Now, a continuous girder uniformly loaded 



498 STEAM-BOILERS, 

with w pounds per inch of length, which has a middle span / 
inches long, and two end spans £/ inches long, will have for 
the end-supporting forces \\\wl, and for the middle support- 
ing forces f$Jtt//. The end supporting forces are provided 
by the shell, which is abundantly able to carry them. The 
stay-rods, which furnish the middle-supporting forces, must 
each carry 

Hi X I5l X 1387.5 = 21,083 pounds. 

Assuming a working-stress of 9000 pounds per square inch 
for the stay, the area of the section for a stay is 

21,083 -T- 9000 = 2.34 

square inches. The corresponding diameter is not quite ifj- 
of an inch. As rods of this size are not regularly carried in 
stock, we will take the next larger regular size, namely, ij 
of an inch. This is the size mentioned in connection with the 
discussion of the lower stay-rods. 

Upper Channel-bar. — The calculation of the stress in the 
upper channel-bar will be made by an extension of the same 
approximate method used with the lower channel-bar. Since 
the middle span is wider than the end spans, it will be suffi- 
cient to make a calculation for it only. The calculation is 
made as for a simple beam supported at the ends, the points 
of support being at one fourth of the diameter of the thick 
washer from the middle stay-rod, that is, at the distance of 
if of an inch from the stay-rod. The distance between the 
upper stay-rods is 15J inches, so that the span of the beam is 

I5|- 2 X if = I2f inches. 

The beam is assumed to be loaded with concentrated loads 
applied at the rivets C, D, E, F, G, and H (Fig. 228); the 
load on the rivet / is assumed to be carried by the stay-rod 
directly, and is not included in this calculation. The pair of 



BOILER DESIGN. 499 

rivets D and E, and the several rivets C, G, and H, are 
assumed to carry the load due to the pressure on the areas 
marked off by the dotted lines on Fig. 228 each line being 
drawn half-way between adjacent supporting points, except 
that the arc at the top is drawn 3^ inches from the shell, as 
already said. The calculation of the loads on these rivets, of 
the supporting forces, and of the bending moments is simple 
and direct, but is tedious when stated in detail. We will 
therefore be contented to say that the bending moment at 
the middle of the beam is 37,390. Taking, as with the lower 
channel-bar, a working-stress of 16,000 pounds, we have 

16,000/ / 

37>39° = > or - =2.17. 

The makers of steel beams, channel-bars, and angle-irons 
publish handbooks which give the sizes and properties of the 
standard forms, including the moment of inertia / and the 

ratio -, which is called the moment of resistance. From such 

y 

a handbook it appears that the moment of resistance of the 
channel-bar 6" X 2\" X \" is 1.08, and that the moment 
of resistance of the 3^ // X 3" angle-iron is 1.55; the sum 
2.63 is larger than the required moment of resistance given 
above. These forms are consequently used as shown on 
Plate I. 

Brackets. — The boiler shown on Plate I is supported on 
four cast-iron brackets, each of which is 10 inches wide in the 
direction of the length of the boiler, and 15J inches long 
measured circumferentially. Each bracket is riveted to the 
shell by nine rivets 15/16 of an inch in diameter. Boilers 
over 16 feet long commonly have six brackets. The brackets 
are made wide and long in order that the local strains due to 
carrying the weight of the boiler may not be excessive. The 
rivets are larger than are used about the boiler, as the pitch is 
not restricted as in a calked seam. 



5 00 STEAM-BOILERS. 

The brackets are set above the middle line of the boiler 
so that the flanges may be protected by brickwork. In the 
case in hand they are 3^ inches above the middle; as much 
as 4^ inches is commonly used. 

The brackets are arranged so that the weight of the boiler 
and accessories is equally divided among them, and so that 
there is as little bending-moment as possible on the shell of 
the boiler. When four brackets are used they may be some- 
what less than a fourth of the length of a tube, from the tube- 
plates. 

The load on the brackets may be estimated by calculating 
the weight of the boiler when entirely full of water, and add- 
ing the weight of all parts that are supported by the boiler, 
such as pipes, valves, and brickwork or covering, that may 
rest on the boiler. One fourth of this load is assigned to each 
bracket. This load on a bracket should be uniformly dis- 
tributed over the bearing-surface of the flange, which is com- 
monly 8 or 9 inches wide. But to guard against the effect of 
unequal bearing, it is well to assume the bracket to bear near 
the outer edge — say two inches from the edge. Such an 
assumption will bring the bearing-force on a bracket on 
Plate I, 10 inches from the shell. This bearing-force tends 
to rotate the bracket about its upper edge, and this tendency 
is resisted by the rivets under the flange, which must be large 
enough to resist the resulting pull on them. The other rivets 
are added to give sufficient resistance to shearing all the 
rivets. There are seldom less than nine rivets in a bracket, 
all as large as those below the flange, even though fewer would 
suffice. The bracket is usually made of cast iron, and the 
dimensions are commonly controlled as much by the condi- 
tions required for a sound casting as by calculations for 
strength. The strength may be calculated, treating it as a 
cantilever, allowing for the web connecting the flange to the 
body of the casting. 

Specifications and Contract. — The engineer intrusted 



BUILER DESIGN. r OI 

with the design of a boiler prepares a set of working drawings 
and a set of specifications which give all necessary instructions 
concerning the material to be used and the methods of con- 
struction to be followed. The drawings and specifications 
form a part of the contract with the boiler-maker. 

Boiler-makers commonly design standard forms of boilers, 
and in answer to inquiry will furnish a statement or set of 
specifications for a desired boiler in form of a letter, which 
letter forms the contract for the boiler. On the next page is 
given the contract and specifications for the boiler shown on 
Plate I. 



502 STEAM-BOILER. 



IRON WORKS CO. 



Boston, Mass., Feb. /, 1897. 



Gentlemen : 



Your letter of received. We will build 

One (/) Horizontal Tubular Boiler. One Boiler, viz., Sixty (bo) inches diameter by 
seventeen 2/12 (17&) feet iong. Containing 84 Tubes 3 inches diameter, by sixteen (ib) feet 
long. Shell of Boiler of O. H. Fire-box Steel, y/ib" thick, not less than 33,000 nor over 60,000 
lbs. Tensile Strength. Not less than 36% reduction 0/ area, and 23% elongation in 8". 

Heads of Boiler of O.H. Flange Steel q/ib" thick. Longitudinal Seams Butt Jointed, 
with double covering-plates, Triple Riveted. Rivet-holes drilled in place, i.e., Rivet-holes 
punched i / 4" small, courses rolled up, covering-plates bolted on courses. Heads in courses 
■with all holes together perfectly fair. Then rivet-holes drilled to full size. 

Longitudinal braces without welds, with upset screw ends. 

Two (2) or three (3) Lugs on each side, and to be provided with wall-plates and expan- 
sion-rolls. Manhole (internal frame) on top. This frame a steel casting. 



Two (2) 5" Nozzle* on top, 



A Hand-hole in each head, Fusible Safety Plug in back head. Bottom at back end 

reinforced and tapped for 2" blowout 

Internal Feed Pipe placed in Boiler Co.'s style, 

With Boiler, Castings for setting, viz.; C. I., Overhung Front, Mouth-pieces, 
Division Plates, Grate Bars, shaking pattern bo" X bo" . Grate Bearers, Ash-pit Door for 
the brickwork, Back Return Arched T Bars, the Anchor Bolts for Front. One (1) set of 

six (6) Buckstaves and Tie Rods with the boiler. With the Boiler One (1) 4" Pop 

Safety Valve, (3)3/4" Gauge Cocks, One (1) b" Steam Gauge, One (1)3/4" Water Gauge and 

One (1) Combination Column Boiler tested 223 lbs. per 

square inch. Inspected and Insured in the sum of $400.00 for one year, by Steam 

Boiler Inspection & Insurance Co 

The Boiler Castings and Fixtures as herein specified by name, delivered F. O. B. cars, 
or at vessel's wharf, or on sidewalk of building, Boston, Mass., for the sum of six hundred 
and seventy (byo.oo) dollars net. 

Very respectfully yours, 

IRON WORKS CO. 

P. S. — Specimens will be furnished, one lengthwise and one crosswise, from each plate. 
To be at least 18" long and planed on edge 1" or i\" wide. These specimens shall show no 
blowhole defects and shall bend double cold, at a red heat, and at a flanging heat. 



APPENDIX. 



50.3 



5°4 



APPENDIX. 















HORIZONTAL RETURN TUBULAR 






Heat- 
ing- 
Surface 


Shell. 


Tubes. 




















Number. 


No. 


Horse- 
power. 


Diam- 
eter. 


Length, 
O. H. 


Length, 
Flush. 


Length, 


Diam- 
eter. 


With 
Man- 


With- 
out 
























hole. 


Man- 
hole. 


I 


21 


254 


36 


11 





11 





10 





3 




28 


2 


25 


3°4 


36 


J 3 





13 





12 





3 




28 


3 


33 


403 


42 


13 





J 3 





12 





3 




38 


4 


39 


469 


42 


15 





15 





14 





3 




38 


5 


55 


604 


48 


15 


2 


15 


2 


14 





3 




50 


6 


62 


690 


48 


17 


2 


17 


2 


16 





3 




50 


7 


49 


548 


48 


15 


2 


15 


2 


14 





3h 




38 


8 


56 


625 


48 


17 


2 


17 


2 


16 





3h 




38 


9 


67 


739 


54 


15 


2 


15 


2 


14 





3 




62 


IO 


76 


844 


54 


17 


2 


17 


2 


16 





3 




62 


ii 


86 


949 


54 


19 


2 


19 


2 


18 





3 




62 


12 


64 


704 


54 


i5 


2 


15 


2 


14 





3h 




5° 


13 


73 


803 


54 


17 


2 


17 


2 


16 





3h 




50 


14 


82 


9°3 


54 


19 


2 


19 


2 


18 





3l 




50 


15 


87 


875 


60 


15 


2 


15 


2 


14 


O 


3 


74 


82 


16 


99 


999 


60 


17 


2 


17 


2 


16 





3 


74 


82 


i7 


112 


1123 


60 


19 


2 


19 


2 


18 





3 


74 


82 


18 


76 


765 


60 


15 


2 


15 


2 


14 





3i 


54 


62 


19 


87 


873 


60 


17 


2 


17 


2 


16 





3* 


54 


62 


20 


98 


981 


60 


19 


2 


19 


2 


18 





3* 


54 


62 


21 


124 


1247 


66 


17 


6 


17 


2 


16 





3 


94 


104 


22 


140 


1401 


66 


19 


6 


19 


2 


18 





3 


94 


104 


2 3 


i55 


1556 


66 


21 


6 


21 


2 


20 





3 


94 


104 


24 


113 


ii33 


66 


i7 


6 


17 


2 


16 





3* 


72 


80 


25 


127 


1273 


66 


19 


6 


19 


2 


18 





3i 


72 


80 


26 


141 


1414 


66 


21 


6 


21 


2 


20 





3* 


72 


80 


27 


99 


996 


66 


17 


6 


17 


2 


16 





4 


54 


62 


28 


111 


1119 


66 


19 


6 


19 


2 


18 





4 


54 


62 


29 


124 


1242 


66 


21 


6 


21 


2 


20 





4 


54 


62 


30 


158 


1588 


72 


17 


6 


17 


2 


16 





3 


122 


130 


31 


178 


1785 


72 


19 


6 


19 


2 


18 


O 


3 


122 


130 


3 2 


198 


1982 


72 


21 


6 


21 


2 


20 





3 


122 


130 


• 33 


144 


1448 


72 


17 


6 


17 


2 


16 





3* 


94 


102 


34 


162 


1628 


72 


19 


6 


19 


2 


18 





3i 


94 


102 


35 


180 


1807 


72 


21 


6 


21 


2 


20 





3* 


94 


102 


36 


129 


1292 


72 


17 


6 


17 


2 


16 





4 


72 


80 


37 


145 . 


i45 2 


72 


19 


6 


19 


2 


18 





4 


72 


80 


38 


161 


1612 


72 


21 


6 


21 


2 


20 





4 


72 


80 


39 


209 


2090 


78 


19 


6 






18 





3 


144 


i54 






40 

41 
42 

43 

44 

45 
46 

47 


232 

195 

216 


2321 

1952 
2167 
1821 


78 
78 
78 
78 
78 
84 
84 
84 


21 


6 






20 





3 

3i 

3* 

4 

4 

3 

3 

3} 


144 


*54 


19 
21 


6 




18 


O 


114 


122 


6 




20 





114 


122 


182 


19 
21 


6 




18 





92 

92 

180 


100 


202 


2022 


6 




20 





100 


257 
286 
236 


2579 
2864 
2367 


19 
21 


6 




18 


O 


190 


6 




20 





180 


190 
1 5° 


19 


6 




18 





140 








48 
49 


262 
215 


2629 

2i55 


84 
84 


21 


6 






20 





3* 
4 


140 


*5° 


19 


6 




18 





no 


114 








5° 


239 


2302 


84 


21 


6 






20 





4 


no 


114 







APPENDIX. 



505 



BOILERS. 


(ROBB-MUMFORD BOILER Co.) 










Thickness, 
125 Pounds. 


Thickness. 
150 Pounds. 


Size 

of 

Safety 


Grates. 


Weights. 






















Shell. 


Heads 


Style 
Joint. 


Shell. 


Heads 


Style 
Joint. 


Valve 


Width 


L'gth 


Boiler 
Only. 


Castings. 


Total. 


1/4 


3/8 


D.L. 










2 


36 


3° 


2730 


2030 


4760 


1/4 


3/8 


D.L. 











2 


36 


36 


3120 


2080 


5200 


S/16 


3/8 


D.B. 


n/32 


3/8 


D.B. 


2 


42 


36 


4670 


2670 


7340 


5/l6 


3/8 


D.B. 


11/32 


3/8 


D.B. 


2 


42 


42 


5270 


2740 


8010 


11/32 


7/16 


D.B. 


13/32 


7/16 


D.B. 


2i 


48 


42 


6800 


3540 


10340 


H/32 


7/16 


D.B. 


13/32 


7/16 


D.B. 


2h 


48 


48 


758o 


4000 


1 1 580 


11/32 


7/16 


D.B. 


13/32 


7/16 


D.B. 


2* 


48 


42 


6740 


3540 


10280 


n/32 7/16 


D.B. 


13/32 


7/16 


D.B. 


2* 


48 


48 


7520 


4000 


1 1 520 


11/32 7/16 


T.B. 


13/32 


7/16 


T.B. 


2§ 


54 


48 


8120 


4300 


12420 


11/32 7/16 


T.B. 


13/32 


7/16 


T.B. 


3 


54 


54 


9100 


4770 


13870 


11/32 7/16 


T.B. 


13/32 


7/16 


T.B. 


3 


54 


60 


1 0000 


5*9° 


15190 


11/32 7/16 


T.B. 


13/32 


7/16 


T.B. 


*\ 


54 


48 


8210 


4300 


12510 


11/32; 7/16 


T.B. 


13/32 


7/16 


T.B. 


3 


54 


54 


9210 


4770 


13980 


n/32 7/16 


T.B. 


13/32 


7/16 


T.B. 


3 


54 


60 


10120 


5 J 9o 


IS3IO 


3/8 


1/2 


Q.B. 


7/l6 


1/2 


Q.B. 


3 


60 


54 


10270 


4920 


1 5190 


3/8 


1/2 


Q.B. 


7/16 


1/2 


Q.B. 


3 


60 


60 


11420 


53°° 


16720 


3/8 


1/2 


Q.B. 


7/16 


1/2 


Q.B. 


3 


60 


66 


12480 


594o 


18420 


3/8 


1/2 


Q.B. 


7/16 


1/2 


Q.B. 


3 


60 


54 


10060 


4920 


14980 


3/8 


1/2 


Q.B. 


7/16 


1/2 


Q.B. 


3 


60 


54 


1 1 180 


5*7° 


16250 


3/8 


1/2 


Q.B. 


7/i6 


1/2 


Q.B. 


3 


60 


60 


12200 


579o 


17990 


I3/3 2 


1/2 


Q.B. 


15/32 


1/2 


Q.B. 


3 


66 


60 


14500 


579o 


20290 


I3/3 2 


1/2 


Q.B. 


15/32 


1/2 


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3h 


66 


66 


1593° 


6410 


22340 


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72 


17380 


6540 


23920 


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1/2 


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3 


66 


60 


14410 


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3 


66 


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6170 


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3i 


66 


66 


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21780 


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17170 


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23710 


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72 


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7290 


26200 


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4 


72 


84 


20650 


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23640 


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26110 


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78 


20560 


7440 


28000 


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66 


16960 


6540 


23500 


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66 


18670 


7150 


25820 


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72 


72 


20390 


7290 


27680 


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9/i6 


T.B. 


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4 


78 


78 


22580 


8550 


3 1 *3° 


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T.B. 


9/16 


9/16 


Q.B. 


4 


78 


90 


24620 


8860 


3348o 


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9/i6 


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9/16 


Q.B. 


4 


78 


78 


22710 


8550 


31260 


1/2 


9/16 


T.B. 


9/16 


9/16 


Q.B. 


4 


78 


84 


24770 


8660 


33430 


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9/16 


9/16 


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4 


78 


72 


22960 


8400 


3 1 3 6 ° 


1/2 


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9/16 


9/16 


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4 


78 


78 


25060 


8550 


33 6 io 


1/2 


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5/8 


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4t 


90 


84 


25700 


9440 


35140 


1/2 


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5/8 


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4l 


90 


96 


28100 


9790 


37890 


1/2 


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5/8 


Q.B. 


4* 


90 


84 


25670 


9440 


35i 10 


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Q.B. 


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5/8 


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90 


90 


28070 


9620 


37690 


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5/8 


Q.B. 


4* 


90 


78 


25700 


9260 


34960 


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4* 


90 


84 


28110 


0440 


37550 



506 



APPENDIX. 










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APPENDIX. 



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M 



APPENDIX. 



509 



Stirling Boilers. — These boilers clean from the side, the 
same as the B. & W., and only two can be set together without a 
space between. If necessary the boiler may be set without a 
space at the back, but it is advisable to have at least 3 feet 
back of the rear wall. 

These boilers are also built with attached superheaters. The 
superheater is placed at different parts of the setting, according 
to the number of degrees of superheating desired. 

The following table gives dimensions of this boiler for different 
boiler horse-powers. 

If the boiler is equipped with a superheater, deduct 10 per 
cent from the rated horse-power. If, however, the superheater 
is flooded the capacity of the boiler is increased approximately 
7 per cent above the ratings given. 

HORSE-POWER OF STIRLING BOILERS. 

Arranged with Reference to Height and Width of Settings. 





Class. 


Width of 


1 1 
















Setting. 


B-low.l P j E 


1 B | A 


1 Q 


1 F 


1 R 


1 K 


1 L 


1 N 




Height. 






ii'n"|i5'4£'ii5' 3" 


|i 5 ' 8"|i8' 9" 


|i8'io" 


[20' 7" 


1 20' 8" 


|ai'io" 


I22' 4" 


I24' 6" 


Single. 


Bat- 
tery.* 

feet. 






Depth 












ft in. 


14' 0" 


18' 7" 


16' 3" 


14' 0" 


1 6' 0" 


18' 9" 


16 9 


1 8' 2" 


17' 7" 


18' y 


18 10" 


5 6 


10 


50 


... 


... 


50 
















6 


11 


55 




75 


60 
















6 6 


12 


65 




90 


70 
















7 


13 


75 


115 


100 


80 


115 


145 


140 


145 


150 


165 


175 


7 6 


14 


85 


130 


115 


90 


130 


165 


155 


160 


170 


185 


195 


8 


15 


95 


145 


125 


100 


145 


180 


175 


180 


185 


205 


220 


8 6 


16 


105 


160 


140 


no 


160 


200 


190 


200 


205 


230 


240 


9 


17 


115 


175 


150 


120 


175 


215 


205 


215 


225 


250 


260 


9 6 


18 


125 


190 


165 


130 


190 


235 


225 


235 


245 


270 


285 


10 


J 9 


i35 


205 


i75 


140 


205 


255 


240 


250 


260 


290 


305 


10 6 


20 


140 


220 


190 


150 


215 


270 


260 


270 


280 


310 


33° 


11 


21 


1 5° 


230 


200 


160 


230 


290 


275 


285 


300 


33° 


35o 


11 6 


22 


160 


245 


215 


170 


245 


310 


295 


3°5 


315 


35o 


37o 


12 


23 


170 


260 


225 


180 


260 


325 


310 


325 


335 


37o 


395 


12 6 


24 


180 


275 


240 


190 


275 


345 


33° 


34o 


355 


395 


4i5 


13 


25 


190 


290 


250 


200 


290 


3 6 ° 


345 


360 


375 


4i5 


435 


13 6 


26 


200 


3°5 


265 


210 


305 


380 


360 


375 


39° 


435 


460 


14 


27 


210 


320 


275 


220 


320 


300 


380 


395 


410 


455 


480 


14 6 


28 


220 


335 


290 


230 


335 


4i5 


395 


410 


43° 


475 


5o5 


15 ° 


29 


230 


35° 


300 


240 


35o 


435 


4i5 


43° 


45° 


495 


525 


15 6 


3° 


240 


365 


3i5 


250 


360 


45° 


43° 


45° 


465 


5i5 


545 


16 


3i 


250 


375 


33o 


260 


375 


470 


45o 


465 


485 


54o 


57° 


16 6 


3 2 


260 


39° 


34o 


270 


39o 


490 


465 


485 


" 5o5 


560 


59° 


17 


33 


265 


405 


355 


280 


405 


5o5 


485 


505 


520 


580 


610 


17 6 


34 


275 


420 


365 


290 


420 


525 


500 


520 


540 


600 


635 


18 


35 


285 


435 


380 


300 


435 


545 


515 


540 


560 


620 


655 


*The hors 


^e-power is double i 


or battery w 


idth si 


iown. 


Single 


boiler 


s requ 


ire an 


alley on 


one sic 


e; bat 


ery bo 


tiers re 


luire a 


1 alley 


on bot 


1 sides 











5 IQ 



APPENDIX. 



Heine Water Tube Boiler. — This boiler requires a space at 
the back as it is cleaned from the ends. Any number of boilers of 
this type can be set side by side. 

The space in front of the boiler should be sufficient to allow of the 
renewal of a tube. 

The accompanying table together with the "Notes" will serve to 
give necessary sizes for a given boiler horse-power. 

Notes. 

The length of setting from fire front to rear of brickwork is always 
i foot 4 inches longer than the length of the tubes, for instance, the 
setting of a 90 horse-power boiler is 17 feet 4 inches long and a 101 horse- 
power boiler is 19 feet 4 inches long. The shell with manhead extends 
about 15 inches beyond rear of setting, so that if possible a 4-foot space 
should be allowed behind the setting for access to same. In special 
cases the manhole is placed in the front head, or an opening may be 
made in the building wall opposite manhole, in which case 2 feet 
behind setting will be sufficient. The width of setting may be deter- 
mined by adding the thickness of brick walls to the width of furnace. 
Thus, three 101 horse-power boilers in a battery, with 19 inches side 
and 28 inches division walls, will be 19" + 53"+ 28"+ 53"+ 28"+ 53" 
+ 19"= 21' 1". Existing walls may be utilized where space is limited, 
and the outside walls here reduced to a furnace lining 9 or 10 inches 
thick. 

The grate-surface given for bituminous coal is such that the rating 
may be easily developed with a 1/2-inch draught at the smoke outlet. 
The grate area given for anthracite pea coal is that necessary in order 
to develop the rating of the boiler with 1/2-inch draught at the smoke 
outlet. For convenience of handling it is advisable to limit the grate 
length for anthracite coal to 7 feet 6 inches. Where this does not give 
area enough for the desired maximum capacity it is necessary to in- 
crease the draught. Standard grate lengths are 6 feet 6 inches, 7 feet 
and 7 feet 6 inches. 

Safety-valves are provided as required to meet local inspection laws. 



Babcock and Wilcox Boilers. — These boilers clean from the 
side. There must be a space of at least 5 feet between each set of two. 

The tables on pages 405 and 406 give space taken up by boilers with 
vertical headers. For inclined headers, any number of tubes high, add 
3 feet 8 inches to the length given. 

A double-deck boiler is 10 inches higher than a single-deck boiler 
of same number of tubes high. 

Space must be left in front of the boiler to enable the lowest tube to 
be replaced. 



APPENDIX. 



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5i2 



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APPENDIX. 



513 





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•A^axxvg aNQ NI sxa-iiog; oavx 







APPENDIX. 
GREEN'S FUEL ECONOMIZER. 



515 









Dimensions, 


Area between 




c 


£. 




Valves. 






«-£ 


Inside Walls. 


Tubes. 




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■ s 

s 


8.9 & 




14 




01 


•-so a 
* 




III 



^ Q 


to 



* 


3 


3 
oq 


z 


Feet. 


Feet. 


Feet. 


Feet. 


Feet. 


Feet. 


Feet. 




Sq.ft. 


Lbs. 


E H. 
P. 


Inches. 


32 


4 


4-10 


3-4 


4-1 


4-10 


16.6 


23,85 


31.10 


8 


384 


1,984 


• 5 


2 


i-5 


48 


4 


7- 3 


























12 


576 


2,976 


•5 


2 


i.5 


64 


4 


9- 8 


























16 


768 


3,968 


• 5 


2 


1 -5 


80 


4 


12- 1 


























20 


960 


4,960 


•5 


2 


1.5 


96 


4 


14-6 


























24 


1152 


5.952 


I 


2 


1.5 


JI2 


4 


1 6-1 1 


























28 


1344 


6,944 


1 


2 


i.5 


128 


4 


19- 4 


























32 


1536 


7,936 


1 


2 


1. 5 


144 


4 


21-9 


























36 


1728 


8,928 


1 


2.5 


2 


l6o 


4 


24- 2 


























40 


1920 


9,920 


2 


2.5 


2 


176 


4 


26- 7 


























44 


21 12 


10,912 


2 


2.5 


2 


192 


4 


29- 


























48 


2304 


11,904 


2 


2.5 


2 


208 


4 


3i- 5 














52 


2496 


12,896 


2 


2.5 


2 


48 


6 


4-10 


4-8 


5-5 


6-2 


21.85 


29. 10 


3 6 -.3 5 


8 


576 


2,976 


•5 


2 


X S 


72 


6 


7- 3 


























12 


864 


4,464 


• 5 


2 


1 5 


96 


6 


9- 8 


























16 


1152 


5,852 




2 


i-5 


I20 


6 


12- 1 


























20 


1440 


7,440 


1 


2 


i-5 


144 


6 


14-6 


























24 


1728 


8,928 


1 


2-5 


2 


168 


6 


16-11 


























28 


2016 


10,416 


2 


2.5 


2 


192 


6 


19- 4 


























32 


2304 


11,904 


2 


2.5 


2 


2l6 


6 


21-9 


























36 


2592 


13.392 


2 


2-5 


2 


240 


6 


24- 2 


























40 


2880 


14,880 


2 


2-5 


2 


264 


6 


26-7 


























44 


3168 


16,368 


2.5 


2-5 


2 


288 


6 


29- 


























48 


3456 


17,856 


2-5 


2.5 


2 


312 


6 


3i- 5 


























52 


3744 


19,344 


2.5 


2.5 


2 


336 


6 


33-IO 


























56 


4032 


20,832 


2 -5 


2-5 


2 


360 


6 


36- 3 














60 


4320 


22,320 


3 


3 


2.5 


96 


8 


7- 3 


6-0 


6-9 


7-6 


27.00 


34.25 


4i... 5 


12 


1152 


5,952 


1 


2 


1 -5 


128 


8 


9- 8 


























16 


1536 


7,936 


1 


2 


i-5 


l6o 


8 


12- 1 


























20 


1920 


9,920 


2 


2.5 


2 


192 


8 


14-6 


























24 


2304 


11,904 


2 


2-5 


2 


224 


8 


1 6-1 1 


























28 


2688 


13,888 


2 


2-5 


2 


256 


8 


19- 4 


























32 


3072 


15,872 


2 


2.5 


2 


288 


8 


21- 9 


























36 


3456 


17,856 


2-5 


2.5 


2 


320 


8 


24- 2 


























40 


3840 


19.840 


2-5 


2.5 


2 


352 


8 


26— 7 


























44 


4224 


21,824 


2-5 


3- 


2.5 


384 


8 


29-0 


























48 


4608 


23,808 


2.5 


3 


2-5 


416 


8 


3i- 5 


























52 


4992 


25,792 


2-5 


3 


2-5 


448 


8 


33-io 


























56 


5376 


27,776 


3 


3 


2.5 


480 


8 


36- 3 














60 


576o 


29,760 


3 


3 


2-S 


160 


10 


9- 8 


7 ." 4 


8-1 


8-10 


32.25 


39 4 -.5o 


46.75 


16 


1920 


9,920 


2 


2-5 


2 


200 


10 


12- 1 


























20 


2400 


12,400 


2 


2-5 


2 


240 


10 


14- 6 


























24 


2800 


14,880 


2 


2-5 


2 


280 


10 


1 6-1 1 


























28 


336o 


17,360 


2-5 


2-5 


2 


320 


10 


19- 4 


























32 


3840 


19,840 


2-5 


3- 


2-5 


360 


10 


21- 9 


























36 


4320 


22,320 


2.5 


3- 


2-S 


400 


10 


24— 2 


























40 


4800 


24,800 


2.5 


3- 


2-5 


440 


10 


26- 7 


























44 


5280 


27,780 


2.5 


3- 


2-5 


480 


10 


29- 


























48 


576o 


29,780 


2.5 


3- 


2.5 


520 


10 


3i- 5 


























52 


6240 


32,240 


3 


3. 


2-5 


560 


10 


33-IO 


























56 


6720 


34,720 


3 


4. 


3 


600 


10 


36- 3 


























60 


7200 


37,200 


3 


4. 


3 


640 


10 


38- 8 


























64 


7680 


39,680 


3 


4. 


3 


680 


10 


41- 1 


























68 


8160 


42,160 


3 


4. 


3 


720 


10 


43- 6 


























72 


8640 


44,640 


4-5 


4. 


3 


760 


10 


45-n 


























76 


9120 


47.120 


4-5 


4. 


3 


800 


10 


48- 4 














80 


96oo|49,6oo 

1 


5 


4- 

/ 


3 



5i6 



APPENDIX. 



STANDARD SIZES OF STURTEVANT 



Ma- 
chine 
No. 



I 
2 

3 
4 
5 
6 

7 
8 

9 

io 
ii 

12 

13 
14 
i5 
16 

i7 
18 

i9 

20 
21 
22 
23 

24 

25 
26 

27 
28 
29 

3° 
31 
32 
33 
34 
35 
36 
37 
38 
39 
40 

4i 
42 

43 

44 
45 
46 

4? 
48 
49 



No. 

of 
Pipes. 



3 2 
48 
64 
80 
96 
112 
128 
40 
60 
80 
100 
120 
140 
160 
180 
200 
72 
9 6 
120 
144 
168 
192 
216 
240 
264 
288 
112 
140 
168 
196 
224 
252 
280 
308 
33 6 
3 6 4 
392 
128 
160 
192 
224 
256 
288 
320 
352 
384 
416 
448 
480 



No. 
of 
Sec- 
tions. 



Ex- 
ternal 
No. of ! Heat- 
Pipes in 1 ing- 
Section. surface. 

Sq. ft. 



8 
12 
16 
20 
24 
28 
32 

8 
12 
16 
20 
24 
28 
32 
36 
40 
12 
16 
20 
24 
28 
3 2 
36 
40 

44 
48 
16 
20 
24 
28 
32 
36 
40 

44 
48 
52 
56 
16 
20 
24 
28 
32 
36 
40 

44 
48 
52 
56 
60 



400 

600 

801 

1001 

1 201 

1401 

1601 

499 

749 

999 

1248 

1499 

1747 
1997 
2247 
2496 

897 
1196 
1496 

1795 
2094 

2393 
2692 
2991 
3290 
3589 
1394 
1743 
2092 
2440 
2789 

3137 
3486 

3835 
4183 
4532 
4880 

I59 2 
1990 

2388 
2786 
3185 
3583 
398i 
4379 
4777 
5i75 
5573 
597i 



Capacity 

in 
Pounds 

of 
Water. 



2,016 

3,° 2 4 

4,032 

5,°4o 

6,048 

7,056 

8,064 

2,520 

3,78o 

5,040 

6,300 

7,56o 

8,820 

10,080 

n,34o 

12,600 

4,536 

6,048 

7,56o 

9,072 

10,584 

12,096 

13,608 

15,120 

16,632 

18,144 

7,056 

8,820 

10,584 

12,348 

14,112 

15,876 

17,640 

19,404 
21,168 
22,932 

24,696 

8,064 

10,080 
12,096 
14,112 

16,128 

18,144 
20,160 
22,176 
24,182 

26,198 

28,224 

30,240 



General Dimensions. 



Length. 



Ft. In. 



4 

7 

9 

12 

14 
16 

19 
4 
7 
9 

12 

14 
16 

19 
21 

24 
7 
9 

12 

14 
16 

19 
21 
24 
26 
29 

9 
12 

14 
16 

19 
21 
24 
26 
29 
3i 
33 
9 
12 

14 
16 

19 
21 

24 
26 

29 
3i 
33 
36 



10 

3 
8 
1 
6 
11 

4 
10 
3 
8 
1 
6 
11 
4 
9 
2 

3 
8 
1 
6 
11 
4 
9 
2 

7 
o 
8 
1 
6 
11 
4 
9 
2 

7 
o 

5 

10 
8 
1 
6 
11 
4 
9 
2 

7 
o 

5 
10 

3 



Width. 



Ft. In. 



3 2* 



3 ioJ 



Height in Feet and 
Inches. 



Section. 



IO 2j 



4 6* 



5 A 



5 i°i 



IO 2\ 



Section 

and 
Gearing. 



IO 2\ 



12 6 
« < 

« < 
«« 



11 

12 6 



APPENDIX. 



5 J 7 



STANDARD 


ECONOMIZERS. 


















No. 




Ex- L 
ternal Capacity 


General Dimensions. 










Height in Feet and 


Ma- 


No. 


No. of 


Heat- ■ ,n . 
ing- Pounds 

surface. „ T °' 

Water. 








Inches. 


chine 
No. 


ox 

Pipes. 


of 


Pipes in 
Section. 


Lciic^^* 


Width. 




Sec- 
tions. 






Section. 


Section 
and 










Sq. ft. 


Ft. 


In. 


Ft. In 




Gearing. 


50 


180 


20 


9 


2,237 ",34° 


12 


I 


6 6J 


IO 2\ 


12 6 


51 


216 


24 


9 


2,685 13,608 


14 


6 






' ' 


52 


252 


28 


9 


3,132 1 15,876 


16 


11 






" 


53 


288 


32 


9 


3,580 18,144 


19 


4 






i < 


54 


3 2 4 


36 


9 


4,027 20,412 


21 


9 






" 


55 


360 


40 


9 


4,475 22,680 


24 


2 






< < 


56 


396 


44 


9 


4,922 ■ 24,948 


26 


7 






« i 


57- 


432 


48 


9 


5,370 27,216 


29 









< < 


58 


468 


52 


9 


5,817 29,484 


31 


5 






< « 


59 


5°4 


56 


9 


6,265 : 3^752 


33 


10 






t < 


60 


540 


60 


9 


6,712 34,020 


36 


3 






< < 


61 


576 


64 


9 


7,160 36,288 


38 


8 






' ' 


62 


200 


20 


10 


2,484 12,600 


12 


1 


7 „ 2 * 


IO 7.\ 


12 6 


63 


240 


24 


10 


2,981 15,120 


14 


6 






" 


64 


280 


28 


10 


3,478 ! 17,640 


16 


11 






( « 


65 


320 


32 


10 


3^974 [ 20,160 


19 


4 






« ( 


66 


360 


36 


10 


4,471 22,680 


21 


9 






• « 


67 


400 


40 


10 


4,968 25,200 


24 


2 






( ( 


68 


440 


44 


10 


5,465 27,720 


26 


7 






" 


69 


480 


48 


10 


5,962 30,240 


29 









*' 


70 


520 


52 


10 


6,458 32,760 


3i 


5 






I ( 


7i 


560 


56 


10 


6,955 35.28o 


33 


10 






( < 


72 


600 


60 


10 


7.45 2 37,8oo 


36 


3 






" 


73 


640 


64 


10 


7.949 


40,320 


38 


8 






" 


74 


680 


68 


10 


8,446 


42,840 


41 


1 






" 


75 


396 


36 


n 


4,9i5 


24,949 


21 


9 


7 M ioJ 


IO 2\ 


12 6 


76 


440 


40 


11 


5,46i 


27,720 


24 


2 






( i 


77 


484 


44 


11 


6,008 


3°,497 


26 


7 






•« 


78 


528 


48 


11 


6,554 


33,268 


29 









" 


79 


572 


52 


11 


7,101 


36,045 


3i 


5 






" 


80 


616 


56 


11 


7,646 


38,811 


33 


10 






<« 


81 


660 


60 


11 


8,i93 


41,588 


36 


3 






< ( 


82 


704 


64 


11 


8,739 


44,359 


38 


8 






" 


83 


748 


68 


11 


9,286 


47,136 


41 


1 






1 


84 


792 


72 


11 


9,832 


49,907 


43 


6 






< 


85 


836 


76 


11 


10,379 


52,684 


45 


11 






t { 


86 


880 


80 


11 


10,925 


55,455 


48 


4 






c ( 


87 


528 


44 


12 


6,549 


33,262 


26 


7 


8 6\ 


IO 2\ 


12 6 


88 


576 


48 


12 


7,145 


36,289 


29 









( « 


89 


624 


52 


12 


7,74i 


39,317 


3 1 


5 






< ( 


90 


672 


56 


12 


8,337 


42,344 


33 


10 






II 


9i 


720 


60 


12 


8,933 


45,37i 


36 


3 






( « 


92 


768 


64 


12 


9,529 


48,398 


38 


8 






** 


93 


816 


68 


12 


10,125 


5i,425 


41 


1 






It 


94 


864 


72 


12 


10,721 


54,452 


43 


6 






(« 


95 


912 


76 


12 


n,3i7 


57,479 


45 


11 






( t 


96 


960 


80 


12 


",913 


60,506 


48 


4 






• 1 


97 


1008 


84 


12 


12,489 


63,432 


5o 


9 






II 


98 


1056 


88 


12 


i3,° 6 5 


66,357 


53 


2 






•4 



i8 



APPENDIX. 
LOGARITHMS. 



Nat. 






















Proportional Parts. 


Nos. 





1 


2 


3 


4 


5 


6 


7 


8 


9 










0000 


0043 


0086 


0128 














1 2 


3 


4 5 


6 


7 8 9 


10 


0170 


0212 


0253 


0294 


0334 


0374 


4 8 


12 


17 21 


25 


29 33 37 


11 


0414 


0453 


0492 


0531 


0569 


0607 


0645 


0682 


07190755 


4 8 


11 


15 19 


23 


26 30 34 


12 


0792 


0828 


0864 


0899 


0934 


0969 


1004 


1038 


1072 1 106 


3 7 


10 


14 17 


21 


24 28 31 


13 


"39 


"73 


1206 


1239 


1271 


1303 


1335 


1367 


1399 1430 


3 6 


10 


13 16 


19 


23 26 29 


14 


1461 


1492 


1523 


1553 


1584 


1614 


1644 


1673 


1703 1732 


3 6 


9 


12 15 


18 


21 24 27 


15 


1761 


1790 


1S18 


1847 


1875 


1903 


i93i 


1959 


1987 2014 


3 6 


8 


11 14 


17 


20 22 25 


16 


2041 


2068 


2095 


2122 


2148 


2175 


2201 


2227 


22532279 


3 5 


8 


11 13 


16 


18 21 24 


17 


2304 


2330 


2355 


2380 


2405 


2430 


2455 


2480 


2504 2529 


2 5 


7 


10 12 


15 


17 20 22 


18 


2553 


2 577 


2601 


2625 


2648 


2672 


2695 


2718 


27422765 


2 5 


7 


9 12 


14 


16 19 21 


19 


2788 
3010 


2810 
3032 


2833 


2856 


2878 


2900 
3118 


2923 
3^39 


2945 
3160 


29672989 
318113201 


2 4 


7 


9 " 


13 


16 18 20 


20 


3054 


3075 


3096 


2 4 


6 


8 11 


13 


15 i7 19 


21 


3222 


3243 


3263 


3284 


3304 


3324 


3345 


3365 


3385 3404 


2 4 


6 


8 10 


12 


14 16 18 


22 


3424 


3444 


3464 


3483 


3502 


3522 


354i 


356035793598 


2 4 


b 


8 10 


12 


14 15 17 


23 


3617 


3636 


3655 


3674 


3692 


37" 


3729 


374737663784 


2 4 


6 


7 9 


11 


13 15 17 


24 


3S02 


3820 


38383856 


3374 


3892 


3909 


3927 


3945 3962 


2 4 


5 


7 9 


11 


12 14 16 


25 


3979 


3997 


40 1 4 '403 1 


4048 


4065 


4082 


4099 


41164133 


2 3 


5 


7 9 


10 


12 14 15 


26 


4150 


4166 


4183 4200 


4216 


4232 


4249 


4265 


4281 4298 


2 3 


5 


7 8 


IO 


11 13 15 


27 


43M 


4330 


43464362 


4378 


4393 


4409 


4425 


44404456 


2 3 


5 


6 8 


9 


11 13 14 


28 


4472 


4487 


45024518 


4533 


4548 


4564 


4579 


4594 4609 


2 3 


5 


6 8 


9 


11 12 14 


29 


4624 
477' 


4639 
4736 


46544669 


4683 


4698 


4713 


4728 


4742 4757 


1 3 


4 


6 7 


9 


10 12 13 


30 


48oo'48i4 


4829 


4843 


4S57 


4871 


4886 4900 


1 3 


4 


6 7 


9 


10 11 13 


31 


49M 


4928 


49424955 


4969 


4983 


4997 


501 1 


5024 5038 


1 3 


4 


6 7 


8 


IO II 12 


32 5051 


5065 


5079I5092 


5105 


5"9 


513- 


5M5 


5I595I72 


1 3 


4 


5 7 


S 


9 II 12 


33 5185 


5198 


5211 5224 


5237 


52505263 


5276 


5289 5302 


* 3 


4 


5 6 


8 


9 IO 12 


34 5315 


5328 


53405353 


5366 


53785391 


5403 


54165428 


1 3 


4 


5 6 


8 


9 10 11 


35 5441 


5453 


5465^478 


5490 


5502 5514 


5527 


5539'555i 


1 2 


4 


5 6 


7 


9 10 11 


36 5563 


5575 


5587 


5599 


5611 


562315635 


5647 


5658 5670 


1 2 


4 


5 6 


7 


8 10 11 


37 5682 


5694 


5705 


5717 


5729 


574U.5752 


5763 


5775 5786 


1 2 


3 


5 6 


7 


8 9 10 


38 579S 


5809 


5821 


5832 


5843 


58555866 


5877 


5888 5899 


1 2 


3 


5 6 


7 


8 9 10 


39 


59" 


5922 


5933 


5944 


5955 


5966 


5977 


5988 


5999 


6010 


1 2 


3 


4 5 


7 


8 9 10 


40 


6021 


6031 


6042 


6053 


6064 


6075 


6085 


6096 


6107 


6117 


1 2 


3 


4 5 


6 


8 9 10 


41 6128 


6138 


6149 6160 


6170 


6180 6191 


6201 


6212 6222 


1 2 


3 


4 5 


6 


7 8 9 


42 6232 


6243 


6253 6263 


6274 


6284^)294 


6304 


63146325 


1 2 


3 


4 5 


6 


7 8 9 


43 '6335 


6345 


6355 


6365 


6375 


63S5|6395 


6405 


64156425 


1 2 


3 


4 5 


6 


789 


44 6435 


6444 


6454 


6464 


6474 


6484.6493 


6503 


6513:6522 


i 2 


3 


4 5 


6 


7 8 9 


45 6532 


6542 


6551 


6561 


6571 


6580 6590 


6599 


6609' 66 1 8 


1 2 


3 


4 5 


6 


7 8 9 


46 6628 


6637 


6646 


6656 


6665 


6675)6684 


6693 


6702 6712 


1 2 


3 


4 5 


6 


7 7 8 


47 6721 


6730,6739 


6749 


6758 


6767 6776 


6785 


67946803 


1 2 


3 


4 5 


5 


678 


48 6812 


6821 6830 


6839 


6848 


6S57 6S66 


6875 


68S4 6893 


1 2 


3 


4 4 


5 


678 


49 6902 


691 1 


6920 
7007 


6928 
7016 


6937 


6946 


6955 


6964 


6972 
7059 


6981 
7067 


1 2 


3 


4 4 


5 


678 


50 


6990 


6998 


7024 


7033 


7042 


7050 


1 2 


3 


3 4 


5 


678 


51 


7076 


7084 


7093 


7101 


7110 


7118 


7126 


7135 


7M3 7152 


1 2 


3 


3 4 


c 


•678 


52 


7160 


7168 


7177 


7185 


7193 


7202 


7210 


7218 


7226 7235 


1 2 


2 


3 4 


c 


6 7 7 


53 


7243 


7251 


7259 


7267 


7275 


7284 


7292 


7300 


730SJ7316 


1 2 


2 


3 4 


5 


667 


54 


7324 


7332 


7340 


7348 


7356 


7364 


7372 


7380 


7388 


'7396 


1 2 


2 


3 4 


5 


667 



APPENDIX. 
LOGARITHMS. 



5*9 



Nat. 
Nos. 





1 


2 


3 


4 






7 


8 


9 


Proportional Parts. 


5 


6 


12 3 


4 5 6 


7 8 9 


55 


7404 


7412 


7419 


7427 


7435 


7443 7451 


7459 


7466 


7474 


122 


3 4 5 


5 6 7 


56 


7482 


7490 


7497 


7505 


75i3 752o|7528 


7536 


7543 


755i 


122 


3 4 5 


5 6 7 


57 


7559 


7566 


7574 


7532 


7589 7597 7604 


7612 


7619 


7627 


i 2 2 


3 4 5 


5 6 7 


58 


76.34 


7642 


7649 


7657 


7664 


7672 7679 


7686 


7694 


7701 


112 


3 4 4 


5 6 7 


59 


7709 


7716 


7723 


773i 


7738 


7745 7752 


7760 


7767 


7774 


1 1 2 


3 4 4 


5 6 7 


60 


7782 


7789 


7796 


7803 


7S10 


78187825 


7832 


7839 


7846 


1 1 2 


3 4 4 


5 6 6 


61 


7853 


7860 


7868 


7375 


7882 


7889 7896 


7903 


7910 


79 J 7 


112 


3 4 4 


5 6 6 


62 


7924 


7931 


7938 


7945 


7952 


7959 79 66 


7973 


798o 


7937 


1 1 2 


3 3 4 


5 6 6 


63 


7993 


Sooo 


8007 


8014 


S021 


8o28;8o35 


8041 


8048 


8055 


1 1 2 


3 3 4 


5 5 6 


64 


S062 

SI2Q 


S069 
S136 


8075 


S082 


8089 


8096 


8102 


8109 


8116 


8122 


1 1 2 


3 3 4 5 5 6 


65 


8142 


8149 


8156 


8162 


Si 69 


8176 


8182 


S189 


1 1 2 


3 3 4 


5 5 6 


66 


Siqq 


8202 


S209 


8215 


8222 


S228 8235 


8241 


8248 


8254 


1 1 2 


3 3 4 


5 5 6 


67 


8261 


3267 


8274 


8280 


8287 


8293 


8299 


8306 


8312 


8319 


1 1 2 


3 3 4 


5 5 6 


6$ 


S325 


8331 


3338 


3344 


3351 


8357 


8363 


3370 


8376 


8382 


112 


3 3 4 4 5 6 


69 


8388 


3395 


8401 


8407 


8414 


8420 


8426 


3432 


8439 


3445 


112 


2 3 4 4 5 6 


7C 


8451 


3457 


8463 


8470 


8476 


8482 


848S 


S494 


8500 


8506 


112 


2 3 4 4 5 6 


71 85t3 


35^9 


8525 


8531 


8537 


8543 3549 


8555 


8561 


3567 


112 


2 3 41 4 5 5 


72 


85 73 


3579 


8585 


8591 


8597 8603 S609 


S615 


S62: 


8627 


1 1 2 


2 3 4, 4 5 5 


73 


8633 


8639 


8645 


8651 


8657 S663 


8669 


3675 


8681 


8686 


112 


2 3 4! 4 5 5 


74 


8692 

8751 


8698 
3756 


8704 
8762 


8710 

8768 


S716 


8722 


8727 


8733 


8739 


8745 


112 


2 3 4 


4 5 5 


75 


3774 


8779 


8785 


8791 


8797 


8S02 


112 


2 3 3 


4 5 5 


76 


8808 


-S14 


8820 


882; 


8831 


8837 8S42 


8848 


S854 


8859 


1 1 2 


2 3 3 


4 5 5 


77 


8865 


S871 


8S76 


S882 


8887 


8S93 SS99 


S904 8910 8915 


1 1 2 


2 3 3 


4 4 5 


78 


8921 


3927 


8932 


8938 


8943 


8949 8954 


S960 S965I8971 


1 1 2 


2 3 3 


4 4 5 


79 


S976 


8982 


8987 


3993 


8998 


9004 9009 


9015 


9020,9025 


1 1 2 


2 3 3 


4 4 5 


80 


9031 


9036 


9042 


9047 


9053 


9058 9063 


9069 


90749079 


1 1 2 


2 3 3 


4 4 5 


81 


9085 


9090 


9096 


9101 


9106 


9112 9117 


9122 


91289133 


1 1 2 


2 3 3 


4 4 5 


82 


9'3« 


9M3 


9149 


9 T 54 


9159 


91659170 


9175 


9180,9186 


112 


2 3 3 


4 4 5 


83 


9191 


9196 


9201 


9206 


9212 


9217 9222 


9227 


9232 


9238 


1 1 2 


2 3 3| 4 4 5 


84 


9243 
9294 


924S 
9299 


9253 
9304 


9258 
9309 


9263 
9315 


92699274 
93209325 


9279 


9284 


9289 


112 


2 3 3 


4 4 5 


85 


9330 


9335 


9340 


1 1 2 


2 3 3 


4 4 5 


86 


9345 


935o 


9355 


9360 


9365 


9370 9375 


93S0 9385 9390 


112 


2 3 3 4 4 5 


87 


9395 


9400 


9405 94io 


9415 


94209425 


9430 9435 9440 


1 1 


223 


3 4 4 


88 


9445 


94509455(9460 


9465 


94699474 


94799484 948g 


1 1 


223 


3 4 4 


89 


9494 


9499 9504;9509 


9513 


95^9523 


95289533953S 


1 1 


2 2 3 


3 4 4 


90 


9542 


954795529557 


9562 


95669571 


95769581 9586 


Oil 


223 


3 4 4 


91 


9590 


9595 9600 9605 


9609 


961419619 


9624'96289633 


Oil 


2 2 3 


3 4 4 


92 


9638 


96439647,9652 


9657 


9661 9666 


9671 


9675 968c 


1 1 


223 


3 4 4 


93 


9685 


9689 


96949699 


9703 


97oS 


9713 


9717 


97229727 


1 1 


223 


3 4 4 


94 


9731 


9736 


974ij9745 


9750 


9754 


9759 


9763 


97689773 


1 1 


223 


3 4 4 


95 


9777 


9732 


97S6'979i 


9795 


9800 


9805 


9809 


9S-4 9S18 


1 1 


223 


3 4 4 


96 


9823 


9827 


9832 9836 


9841 


9845 


9850 


98549S599S63 


1 1 


223 


3 4 4 


97 


9868 


9872 


98779881 


9886 


g3go 9894 


9S99 9903 990S 


1 1 


223 


3 4 4 


98 


9912 


9917 


9921 9926 


9930 


9934 9939 


9943 99439952 


1 1 


223 


3 4 4 


99 


9956 


9961 


9965 


9969 


9974 


9978 


9983 


9987 


9991 


9996 


Oil 


223 


3 3 4 



520 APPENDIX. 

Explanation of the Table for Finding the Area of 
Segment of a Circle. — The areas given in the table are for 
a circle I inch in diameter. The diameter is divided into 
iooo parts, and the area for segments of different heights can 
be taken directly from the table, since the ratio of the height 
of the segment to the diameter of the circle is the same as 
the height of the segment. 

For a circle whose diameter is other than unity. Given 
the diameter of the circle and the height of segment. Re- 
quired area of segment. Divide height of segment by diameter ; 
find area given in the table opposite this ratio ; multiply this 
area by the square of the diameter and the result is the re- 
quired area. 

Example. — Dia. of circle = 60", height of segment =18". 

18 -f- 60 = .30; area in table opposite .30 is . 198 17. 
.19817 X 60 X 60 = area of segment = 713.4 sq. in. 

Given the diameter of the circle and the area of a segment, 
to find the height. 

Divide the area of the segment by the square of the diam- 
eter. Find in the table the area nearest to this, multiply 
the ratio corresponding to this by the diameter of the circle, 
and the result is the required height of the segment. 

Example. — Area of segment = 713.4 sq. in. 

Diameter of circle = 60". Required the height of the 
segment. 

'—— = .19817. Ratio opposite this is .300. 

.300 X 60" = 18", the required height. 

Example — Area of segment = 640 sq. in. 
Diameter of circle — 50". 

640 



= .2560; nearest ratio, .362. 



50 X 50 

.362 X 50 = 18.10", the required height. 



APPENDIX. 521 

TABLE FOR FINDING AREAS OF SEGMENTS OF A CIRCLE. 



" O V 




t; v 




*j O 1) 


j 


«OM 




<-> V 




■a:a 


c 
u 


J3 *j — 

bc w H 


c 
u 




c 

a 

bo 

V 

CO 


sri 


C 

u 


s:a 


c 


£g0 

C 


a 

bX) 

co 


"v c; - ; 


a 

M 
u 

CO 


"5 Ci] 


= |2 

? ° 


a 

bf 
w 

CO 


"S& 


a 

be 

CO 


<u a 




ova 

2 


nj 


v a 
.2 W 1 




« a 

0^1 




.2^2 




rtf 


rtoQ 




is o<5 


U 


« o5 


w 


« oQ 


u 
u 


« oQ 


V 


rt 


< 


a 


< 


« 


< 


tt 


< 


M 


< 


.210 


.II990 


.260 


.16226 


.310 


.20738 


.360 


•25455 


.410 


•30319 


1 


.12071 


1 


.16314 


1 


.20830 


1 


•25551 


1 


•30417 


2 


.12153 


2 


.16402 


2 


.20923 


2 


•25647 


2 


.305x6 


3 


.12235 


3 


.16490 


3 


.21015 


3 


•25743 


3 


•3o6»4 


4 


.12317 


4 


.16578 


4 


.21108 


4 


•25839 


4 


.3071a 


.215 


•12399 


•265 


.16666 


• 31s 


.21201 


.365 


■25936 


•415 


.30811 


6 


.12481 


6 


•l6755 


6 


.21294 


6 


. 26032 


6 


.30910 


7 


.12563 


7 


.16843 


7 


.21387 


7 


.26128 


7 


.31008 


8 


.12646 


8 


.16932 


8 


.21480 


8 


.26225 


8 


.31107 


9 


.12729 


9 


. 1 7020 


9 


•21573 


1 9 


.26321 


9 


•31205 


.220 


.12811 


.270 


.17109 


.320 


.21667 


•370 


.26418 


.420 


•3 T 304 


1 


.12894 


1 


.17198 


1 


. 2 I 760 


1 


•26514 


1 


•334<>3 


2 


.12977 


2 


.17287 


2 


.21853 


2 


.26611 


2 


.31502 


3 


.13060 


3 


.17376 


3 


.21947 


3 


. 26708 


3 


.31600 


4 


•I3M4 


4 


•17465 


4 


. 22040 


4 


.26805 


4 


.31699 


.225 


.13227 


•275 


•17554 


.325 


•22134 


•375 


.26901 


•425 


•31798 


6 


.13311 


6 


.17644 


6 


.22228 


6 


.26998 


6 


•31897 


7 


•13395 


7 


•17733 


7 


.22322 


7 


•27095 


7 


.31996 


8 


•13478 


8 


.17823 


8 


•22415 


8 


.27192 


8 


• 32095 


9 


.13562 


9 


.17912 


9 


.22509 


9 


.27289 


9 


•32194 


.230 


.13646 


.280 


.18002 


•33o 


.22603 


.380 


•27386 


•43° 


•32293 


1 


.13731 


1 


.18092 




.22697 


1 


.27483 




• 32392 


2 


.13815 


2 


.18182 


2 


.22792 


2 


.27580 


2 


•32491 


3 


.13900 


3 


.18272 


3 


.22886 


3 


.27678 


3 


•32500 


4 


.13984 


4 


.18362 


4 


.22980 


4 


•27775 


4 


.32689 


•235 


.14069 


• 285 


.18452 


•335 


•23074 


• 38 | 


.27872 


•435 


•32788 


6 


•I4I54 


6 


.18542 


6 


.23169 


6 


.27969 


6 


.32S87 


7 


•14239 


7 


.18633 


7 


.23263 


7 


. 28067 


7 


•32987 


8 


•^4324 


8 


.18723 


8 


•23358 


8 


.28164 


8 


• 33086 


9 


.T4409 


9 


.18814 


9 


•23453 


9 


.28262 


9 


•33185 


.240 


.14494 


.290 


.18905 


•34o 


•23547 


•39o 


•28359 


•440 


•33284 


1 


.14580 


1 


.18996 


1 


.23642 


1 


•28457 




•33384 


2 


.14666 


2 


.19086 


2 


•23737 


2 


•28S54 


2 


•33483 


3 


•1475 1 


3 


.19177 


3 


•23832 


3 


.28652 


3 


•33582 


4 


.M837 


4 


.19268 


4 


.23927 


4 


.28750 


4 


.33682 


.245 


.14923 


•295 


• 193 6 ° 


•345 


.24022 


•395 


.28848 


•445 


•33781 


6 


■ 15009 


6 


•19451 


6 


.24117 


6 


■28945 


6 


.33880 


7 


•15095 


7 


.19542 


7 


.24212 


7 


.29043 


7 


•3398o 


8 


.15182 


8 


.19634 


8 


•24307 


8 


.29141 


8 


• 34079 


9 


.15268 


9 


.19725 


9 


.24403 


9 


•29239 


9 


•34179 


.250 


•'5355 


.300 


.19817 


•35° 


•24498 


.400 


•29337 


•450 


•34278 


1 


• I 544> 


1 


.19908 


1 


•24593 


1 


•29435 


1 


•34378 


2 


•15528 


2 


. 20000 


2 


.24689 


2 


• 2 9533 


2 


•34477 


3 


.15615 


3 


.20092 


3 


.24784 


3 


•29631 


3 


•34577 


4 


.15702 


4 


.20184 


4 


.24880 


4 


.29729 


4 


.34676 


•255 


•15789 


•305 


.20276 


•355 


.24976 


•405 


.29827 


•455 


•3477 6 


6 


.15876 


6 


.20368 


6 


.25071 


6 


. 29926 


6 


.34876 


7 


•15964 


7 


.20460 


7 


.25167 


7 


.30024 


7 


•34975 


8 


. 16051 


8 


•20553 


8 


•25263 


8 


. 30122 


8 


•35075 


9 


.16139 


9 


.20645 


9 


•25359 


9 


.30220 


9 


•35*75 



522 



APPENDIX 



NATURAL TRIGONOMETRIC 
FUNCTIONS. 



CIRCLES 



Deg. 


Sine. T 


angent. 


Cot. 


Cos. 


Deg. 





.OOOO 


.OOOO 


Infinite 


I. OOOO 


90 


I 


•OI75 


0175 


57.290 


.9998 


89 


2 


•0349 


0349 


28.636 


•9994 


88 


3 


•0523 


0524 


19.081 


.9986 


87 


4 


.0698 


0699 


14-301 


.9976 


86 


5 


.0872 


0875 


11.430 


.9962 


85 


6 


.1045 


1051 


9-5M4 


•9945 


84 


7 


.1219 


1228 


8.1443 


•9925 


83 


8 


.1392 


1405 


7.H54 


•9903 


82 


9 


.1564 


1584 


6.3138 


.9877 


81 


10 


.1736 


1763 


5.6713 


.9848 


80 


ii 


.1908 


1944 


5.1446 


.9816 


79 


12 


.2079 


2126 


4.7046 


.9781 


78 


13 


.2250 


2309 


4.3315 


• 9744 


77 


J 4 


.2419 


2493 


4.0108 


• 9703 


76 


15 


.2588 


2679 


3-7321 


.9659 


75 


16 


.2756 


2867 


3.4874 


.9613 


74 


17 


.2924 


3057 


3.2709 


• 9563 


73 


18 


.3090 


3249 


3.0777 


.9511 


72 


19 


•3256 


3443 


2.9042 


•9455 


7i 


20 


.3420 


3640 


2-7475 


•9397 


70 


21 


.3584 


3839 


2.6051 


.9336 


69 


22 


•3746 


4040 


2.4751 


.9272 


68 


23 


•3907 


4245 


2.3559 


.9205 


67 


24 


.4067 


4452 


2.2460 


• 9135 


66 


25 


.4226 


4663 


2.1445 


.9063 


65 


26 


.4384 


4877 


2.0503 


.8988 


64 


27 


.4540 


5095 


1.9626 


.8910 


63 


28 


.4695 


5317 


1.8807 


.8829 


62 


29 


.4848 


5543 


1 . 8040 


.8746 


61 


30 


.5000 


5774 


1. 7321 


.8660 


60 


3i 


.5150 


6009 


1.6643 


.8572 


59 


32 


.5299 


6249 


1 . 6003 


.8480 


58 


33 


.5446 


6494 


1-5399 


.8387 


57 


34 


•5592 


6745 


1.4826 


.8290 


56 


35 


.5736 


7002 


i.428r 


.8192 


55 


36 


.5878 


7265 


1.3764 


.8090 


54 


37 


.6018 


7536 


1.3270 


.7986 


53 


38 


.6157 


7813 


1.2799 


.7880 


52 


39 


.6293 


8098 


1-2349 


•7771 


5i 


40 


.6428 


8391 


1.1918 


.7660 


50 


4i 


.6561 


8693 


1. 1504 


• 7547 


49 


42 


.6691 


9004 


1.1 106 


•7431 


48 


43 


.6820 


9325 


1.0724 


.7314 


47 


44 


.6947 


9 6 57 


I-Q355 


.7193 


46 


45 


.7071 I 


OOOO 


I. OOOO 


.7071 
Sine. 


45 


Deg. 


Cos. 


Cot. 


Tangent. 


Deg. 



Diam. 


Circumf. 


Area, 


Inches. 


Inches. 


Sq. In. 


12 


371 


113$ 


14 


44 


154 


16 


5o£ 


20I 


18 


56i 


254^ 


20 


621 


3I4| 

38o£ 


22 


69* 


24 


75# 


452| 


26 


8i| 


53i 


28 


88 


6i 5 f 


30 


94i 


7o6| 


32 


ioo| 


8o4i 


34 


io6i 


907| 


36 


"3* 


1017J 


38 


Ii9f 


"34& 


40 


I25f 


1256$ 


42 


132 


i385i 


44 


138^ 


1520^ 


46 


I44| 


i66i| 


48 


I50f 


1809! 


50 


157* 


] 963? 


52 


1 63I 


2123! 


54 


169I 


2290^ 


56 


i75| 


2463 


58 


1824, 


2642J 


60 


i88| 


2827I 


62 


i 94 f 


3019^ 


64 


201 


3217 


66 


207I 


342ii 


68 


213S 


363 if 


70 


219I 


3848^ 


72 


226£ 


4071I 


74 


2 3 2| 


43co£ 


76 


238J 


4536| 


78 


245 


477Sf 


80 


25if 


5026! 


82 


257$ 


5281 


84 


263! 


554if 


86 


2701 


58o8| 


88 


276^ 


608 2£ 


90 


282f 


636lf 


92 


289 


66 4 7£ 


94 


2951 


6939! 


96 


3orf 


7J38* 


98 


307! 


7543 


100 


3I4& 


7854 


102 


32of 


8171* 



APPENDIX. 
ROUND RODS OF WROUGHT IRON. 



5 2 3 









Weight 


Diameter 


Diameter 




Excess of 
Effective 


Diameter 


Circumfer- 


Area in 


of Rod 


of Upset 


of Screw 


Threads 


Area of 


in Inches-. 


ence 
in Inches. 


Sq. Inches. 


One Foot 
Long. 


Screw 
End. 
Inches. 


at Root of 
Thread. 
Inches. 


per Inch. 
Number. 


ScrewEod 
over Bar. 
Per Cent. 




1/16 


.1963 


.0031 


.OIO 










1/8 


.3927 


.0123 


.041 










3/16 


•5890 


.0276 


.092 










1/4 


.7854 


.0491 


. T64 










5/16 


.9817 


.0767 


.256 










3/8 


I.1781 


.1104 


.368 










7/16 


1-3744 


.1503 


.501 










1/2 


1.5708 


.1963 


.654 


3 

1 


.620 


IO 


6* 


9/16 


1 . 7671 


.2485 


.828 


t 


.620 


IO 


21 


5/8 


1.9635 


.3068 


I.023 


7 


.731 


9 


37 


11/16 


2.1598 


.3712 


I.237 


I 


.837 


8 


48 


3/4 


2.3562 


.4418 


1-473 




.837 


8 


25 


13/16 


2.5525 


.5185 


I.728 


T l 


•940 


7 


34 


7/8 


2.7489 


.6013 


2.OO4 


3 


I.065 


7 


48 


I5/I6 


2.9452 


.6903 


2.301 


I.065 


7 


29 


1 


3.1416 


.7854 


2.6l8 


If 


1. 160 


6 


35 


1/16 


3-3379 


.8866 


2-955 


If 


1. 160 


6 


19 


1/8 


3-5343 


.9940 


3-313 


l£ 


I.284 


6 


30 


3/i6 


3.7306 


1. 1075 


3.692 


T l 


I.284 


6 


17 


1/4 


3.9270 


1.2272 


4.O9I 


If 


I.389 


5s 


23 


5/16 


4.1233 


i.353o 


4.510 


If 


I.490 


5 


29 


3/8 


4.3197 


1.4849 


4-950 


T 3 


I.49O 


5 


18 


7/16 


4.5160 


1 .6230 


5.4IO 


I| 


1. 615 


5 


26 


1/2 


4.7124 


1.7671 


5.890 


2 


I. 712 


4l 


30 


5/8 


5-1051 


2.0739 


6.913 


■* 


1.837 


4h 


28 


3/4 


5.4978 


2.4053 


8.018 


4 


1 . 962 


4h 


26 


7/8 


5.8905 


2.7612 


9.204 


2f 


2.087 


4* 


24 


2 


6.2832 


3-1416 


IO.47 


2| 


2.175 


4 


18 


1/8 


6.6759 


3.5466 


11.82 


2| 


2.300 


4 


17 


1/4 


7.0686 


3.9761 


13.25 


2^ 


2-550 


4 


28 


3/8 


7.4613 


4.4301 


14.77 


3 


2.629 


3* 


23 


1/2 


7.8540 


4.9087 


16.36 


3i 


2.754 


3i 


21 


5/8 


8.2467 


5.4II9 


18.04 


3i 


2.879 


3* 


20 


3/4 


8.6394 


5.9396 


19.80 


31 


3.OO4 


3* 


19 


7/8 


9.0321 


6.4918 


21.64 


31 


3.225 


3? 


26 


3 


9.4248 


7.0686 


23.56 


3f 


3.3I7 


3 


22 



524 



APPENDIX. 
LAP-WELDED BOILER-TUBES. 































V 


U 


(A 




c 


is 


£2 


if * 


£3 


fc, « 




j 


aJ 


a 

Q 

£•=■ 
35 


a 
5 _ 

— u? 

C.C 




c 

c/T 

(A 

<u 

c 


11 


-la 

C y 
<U C 
u 1— 1 

11 


<*> 

X 

en „ 

M 

s & 


<£ 

c 
2c/j 


CO <u 

-3 - 

.CCO 03 

bi> £ 
cu *-> 


& ~ 

v- ctf « 

&L £ 


K 

£ c 


c 

1- J 

at; 
be 

c 

£3 . 

s« — 
CO 




u 
V 

0. 


</5 


w 


H 


0" 


o~ 


C-H 


H 


_) 


hJ 


CO 


£ 


z 


i 


.86 


.072 


3-i4 


2.69 


.78 


•57 


3-82 


4.46 


.26 


.22 


•71 


*J4 


iM 


I. II 


.072 


3-93 


3-47 


1.23 


.96 


3 


06 


3 


45 


•33 


.29 


.89 


J/« 




^•33 


.083 


4.71 


4.19 


1.77 


1.40 


2 


55 


2 


86 


•39 


•35 


1.24 


1% 


1.56 


• 095 


5-5o 


4.90 


2.40 


1. 91 


2 


18 


■?. 


45 


.46 


.41 


1.66 


2 


2 


1. 81 


• 09s 


6.28 


5-6g 


3-14 


2-57 


1 


9i 


2 


11 


•52 


•47 


1. 91 


*y A 


2*4 


2.06 


•095 


7.07 


6.47 


3.98 


3-33 


1 


70 


1 


85 


•59 


•54 


2.16 


*y* 

2% 


2% 


2.?8 


.109 


7-8 5 


7.17 


4.91 


4.09 


1 


53 


1 


67 


.65 


.60 


2-75 


2-53 


.log 


8.64 


7-95 


5-94 


5-o3 


1 


39 


1 


51 


•72 


.66 


3-°4 


3. . 


3 


2.78 


.109 


9.42 


8.74 


7.07 


6.08 


1 


27 


1 


37 


•79 


■73 


3-33 


3M 


sM 


3.OI 


.120 


10.21 


9.46 


8.30 


7.12 


1 


17 


1 


26 


.85 


•79 


3-96 


3K 


3*1 


3.26 


.120 


11.00 


10 24 


9.62 


8.35 


1 


09 


1 


17 


.92 


.85 


4.28 


3% 


M 


3-5i 


. 120 


11.78 


11.03 


11.04 


9.68 


1 


02 


1 


09 


.98 


.52 


4.60 


4 


4 


3-73 


.134 


12.57 


11.72 


12.57 


10.94 




95 


1 


02 


1.05 


.98 


5-47 


4^ 


4^ 


423 


•134 


14.14 


13.29 


15.90 


14.07 




85 




90 


1. 18 


1. 11 


6.17 


5 


5 


4.70 


.148 


I5-7I 


14.78 


19.63 


17.38 




76 




81 


"•3» 


1.23 


7-58 


6 


6 


5-6 7 


.165 


18.85 


17.81 


28.27 


25-25 




64 




67 


i-57 


1.48 


10.16 


7 


7 


6.67 


.165 


21.99 


20.95 


38.48 


34-94 




55 




57 


1. S3 


i-75 


11.90 


8 


8 


7.67 


.165 


25-13 


24. 10 


50.27 


46.20 




48 




50 


2.09 


2.01 


13-05 


9 


9 


8.64 


.180 


28.27 


27.14 


63.62 


58.63 




42 




44 


2-35 


2.26 


16.76 


IO 


IO 


9-59 


.203 


31-42 


3 OI 4 


78.54 


72.29 




38 




40 


2.62 


251 


20.99 


ii 


ii 


10.56 


.220 


34 -5 6 


33-17 


95-03 


87.58' 




35 




36 


2.88 


2.76 


25-03 


12 


12 


xx.54 


.229 


37-7° 


36.26 


113-10 


104.63 




32 




33 


3-14 


3.02 


28.46 



SCREW-THREADS. 
Angle of thread 6o°. Flat at top and bottom = £ of pitch. 



Diameter of 


Diameter at 


Threads 


Diameter of 


Diameter at 


Threads 


Screw, 


Root of Thread, 


per Inch, 


Screw, 


Root of Thread, 


per Inch, 


Inches. 


Inches. 


No. 


Inches. 


Inches. 


No. 


Y\ 


.185 


20 


2 


1. 712 


Ate 


% 


.240 


18 


2 H 


1.962 


M 


•294 


16 


2 $ 


2-175 


4 


T 7 5 


•344 


14 


2% 


2-425 


4 


H 


.400 


13 


3 W 


2.629 


3te 


ft 


•454 


12 


■u 


2.879 


M 


•507 


11 


3*3 


3.100 


M 


% 


.620 


10 


■M, 


3-317 


3 


Ve, 


•73i 


9 














4 


3-5°7 


3„, 


1 


.837 


8 


4H 


3.798 


2% 


*X 


•940 


7 


M 


4.028 


2% 


M 


1.065 


7 


4-255 


x% 


1. 160 


6 














5 


4.480 


2^ 


\\ij, 


1.284 


6 


5 H 


4-73Q 




1% 


I-389 


5^ 


ty 


5053 


2?i 


if! 


1.490 


5 


M 


5-203 


2^8 


1% 


1. 615 


5 


6 


5-423 


2J4 



APPENDIX. 525 

WROUGHT-IRON WELDED STEAM-, GAS-, AND WATER-PIPE. 





Diameter. 






Transverse Areas. 


Nominal 


Number of 














Weight 
per 


Threads 
per Inch of 








Thickness. 






Nominal 


Actual 


Actual 




External. 


Internal. 


Foot. 


Screw. 


Internal 


External. 


Internal. 












Inches. 


Inches. 


Inches. 


Inches. 


Sq. In. 


Sq. In. 


Pounds. 




H 


.405 


.27 


.068 


.129 


•0573 


.241 


27 


H 


.543 


• 364 


.088 


.229 


.1041 


.42 


18 


$8 


•675 


• 494 


.091 


.358 


.1917 


•559 


18 


\4& 


.84 


.623 


.109 


•554 


.3048 


.837 


14 


% 


1.05 


.824 


.113 


.866 


•5333 


1. us 


I<t 


I 


i-3*5 


1.048 


• 134 


1-358 


.8626 


1.668 


»H 


M 


1.66 


1.38 


.14 


2.164 


1.496 


2.244 


»*i 


iX 


1.9 


1.611 


.145 


2.835 


2.038 


2.678 


»« 


2 


2-375 


2.067 


•154 


4-43 


3-356 


3.609 


"H 


*& 


2.875 


2.468 


.204 


6.492 


4.784 


5-739 


8 


3 


3-5 


3.067 


.217 


9.621 


7.388 


7-536 


8 


3H 


4- 


3-548 


.226 


12.566 


9.887 


9.001 


8 


4 


4-5 


4.026 


.237 


15.904 


12.73 


10.665 


8 


4^ 


5- 


4.508 


.246 


I9-635 


15-961 


12.34 


8 


5 


5-563 


5-o45 


• 259 


24.306 


19.99 


14.502 


8 


6 


6.625 


6.065 


.28 


34-472 


28.888 


18.762 


8 


7 


7.625 


7.023 


.301 


45.664 


38.738 


23.271 


8 


8 


8.625 


7.982 


.322 


58.426 


50.04 


28.177 


8 


9 


9.625 


8-937 


•344 


72.76 


62.73 


33-701 


8 


10 


10.75 


10.019 


.366 


90.763 


78.839 


40.065 


8 


11 


12 


1125 


•375 


113.098 


99.402 


45-95 


8 


12 


12.75 


12 


•375 


127.677 


113.098 


48.985 


8 


13 


14 


1325 


•375 


153 938 


137.887 


53-921 


8 


H 


15 


14-25 


•375 


176.715 


159.485 


57-893 


8 


15 


16 


15-25 


•375 


201.062 


182 655 


61.77 


8 




18 


1725 
19.25 
21.25 
23.25 


•375 
•375 
•375 
•375 


254-47 
314.16 
380.134 
452-39 


233.706 
291 .04 
354-657 
424.558 


69.66 
77-57 
85.47 
93-37 


















24 









WROUGHT-IRON WELDED EXTRA STRONG PIPE. 



8 


• 405 


.205 


.1 


.129 


•033 


.29 


27 


•54 




294 


.123 


.229 


.068 


•54 


18 


% 


.675 




421 


.127 


.358 


•139 


•74 


18 


/*13 


.84 




542 


.149 


•554 


.231 


1.09 


M 


% 


1.05 




736 


•!57 


.866 


•452 


1.39 


14 


I 


I-315 




95i 


.182 


1-358 


•71 


2.17 


"H 


J H 


1.66 


I 


272 


.194 


2.164 


1. 271 


3 


"*f 


iji 


1.9 


I 


494 


.203 


2.835 


1-753 


3.63 


«fi 


2 


2-375 


I 


933 


.221 


4-43 


2-935 


5.02 


»*i 


*H 


2.875 


2 


3 T 5 


.28 


6.492 


4.209 


7.67 


8 


3 # 


3-5 


2 


892 


•304 


9.621 


6.569 


10.25 


8 


3^ 


4 


3 


358 


.321 


12.566 


8.856 


12.47 


8 


4 


4-5^ 


3 


818 


-341 


I5-904 


11.449 


14.97 


8 


5 


MB 


4 


813 


•375 


24 . 306 


18.193 


20.54 


8 


6 


5-75 


•437 


34.472 


25.967 


28.58 


8 



526 



APPENDIX. 



HEAT OF THE LIQUID. 





B « 




° 




- 









" 







fa 


— "> 


fa 


<*5 


fa 


to 


fa 




fa 


fo 


fa 


«o 


o 


*-« 





«~rs » 





«m3 » 





«~n2 4> 





«~:2» 





•k."^ 4) 




O 3 > 




> 




3 > 




O 3 > 




5 > 




°3 £ 


i 


0)M o3 


a 
S 

0) 


^0*0 

0)1— 1 d 


ft 

a 


0) 1— 1 °3 


ft 

a 

0) 


»M C9 


a 


0)i—! eg 


ft 

a 


Hi 


£ 


ffi 


H 


w 


H 


H 


H 


M 


H 


w 


H 


X 


32 


0.0 


76 


44.1 


121 


89.0 


166 


1340 


211 


179.3 


256 


224.9 


33 


I .0 


77 


45-i 


122 


90.0 


167 


1350 


212 


180.3 


257 


225.9 


34 


2 .O 


78 


46. 1 


123 


91 .0 


168 


136.0 


213 


181. 3 


258 


226.9 


35 


3° 


79 


47-1 


124 


92 .0 


169 


137.0 


214 


182.3 


259 


227.9 


36 


4.0 


80 


48.I 


125 


93 


170 


138.0 


215 


183.3 


260 


229.0 


37 


5 


81 


49-1 


126 


94.0 


171 


139.0 


216 


184.3 


261 


230.0 


38 


6.1 


82 


50.1 


127 


950 


172 


140 .0 


217 


185.3 


262 


231 -o 


39 


7-1 


83 


Si. 1 


128 


96.0 


173 


141 .0 


218 


186.3 


263 


232.0 


40 


8.1 


84 


52.1 


129 


970 


174 


142 .0 


219 


187.4 


264 


2330 


41 


9-i 


85 


53-1 


130 


98.0 


175 


143.0 


220 


188.4 


265 


234 


42 


10. 1 


86 


54-1 


131 


99 


176 


144.0 


221 


189.4 


266 


235.0 


43 


11 . 1 


87 


55-i 


132 


100 .0 


177 


1450 


222 


190.4 


267 


236.1 


44 


12 . 1 


88 


56.1 


i33 


IOI .0 


178 


146 .0 


223 


191. 4 


268 


237.1 


45 


I3-I 


89 


57-1 


134 


102 .0 


179 


147.0 


224 


192 .4 


269 


238.1 


46 


14. 1 


90 


58.1 


i35 


103 .0 


180 


148.0 


225 


193-4 


270 


239.1 


47 


15. 1 


9i 


59-1 


136 


104 .0 


181 


149.0 


226 


194.4 


271 


240.2 


48 


16. 1 


92 


60.1 


137 


105.0 


182 


150. 1 , 


227 


195-4 


272 


241 .2 


49 


17. 1 


93 


61. 1 


138 


106 .0 


183 


151-1 


228 


196.5 


273 


242 .2 


5o 


18. 1 


94 


62 . 1 


139 


107 .0 


184 


152 . 1 


229 


197.5 


274 


243-2 


51 


19. 1 


95 


63.1 


140 


108.0 


185 


153. 1 


230 


198.5 


275 


244.2 


52 


20. 1 


96 


64. 1 


141 


109.0 


186 


154. 1 


231 


199-5 


276 


245-3 


53 


21 . 1 


97 


65.0 


142 


IIO.O 


187 


155. 1 


232 


200.5 


277 


246.3 


54 


22 . 1 


98 


66.0 


143 


III .0 


188 


156. 1 


233 


20T .5 


278 


247-3 


55 


23.1 


99 


67.0 


144 


112 .O 


189 


157.1 


234 


202 .5 


279 


248.3 


56 


24.1 


100 


68.0 


145 


113 .O 


190 


158. 1 


235 


203 .6 


280 


249-4 


57 


25-1 


IOI 


69.0 


146 


114. O 


191 


159.1 


236 


204.6 


281 


250.4 


58 


26.1 


102 


70.0 


147 


IIS.O 


192 


160. 1 


237 


205 .6 


282 


251.4 


59 


27.1 


103 


71.0 


148 


Il6. O 


193 


161 .1 


238 


206.6 


283 


252.4 


60 


28.1 


104 


72.0 


149 


117 .O 


194 


162 . 1 


239 


207 .6 


284 


2 53-4 


61 


29. 1 


105 


73-0 


150 


IlS. O 


195 


163 .1 


240 


208.6 


285 


254.5 


62 


30.1 


106 


74.o 


151 


IIQ. O 


196 


164 . 1 


241 


209 .6 


286 


255.5 


63 


3i. 1 


107 


75.o 


152 


I20.0 


197 


165 . 1 


242 


210.7 


287 


256.5 


64 


32.1 


108 


76.0 


i53 


121 .O 


198 


166.2 


243 


211 .7 


288 


257.5 


65 


33-1 


109 


77.o 


154 


122 .O 


199 


167 .2 


244 


212.7 


289 


258.6 


66 


34-1 


no 


78.0 


155 


I23.0 


200 


168.2 


245 


213-7 


290 


259.6 


67 


35-1 


III 


79-0 


156 


I24.O 


201 


169. 2 


246 


214.7 


291 


260.6 


68 


36.1- 


112 


80.0 


i57 


125 .O 


202 


170.2 


247 


215 7 


292 


261 .6 


69 


37-1 


"3 


81 .0 


158 


I20.O 


203 


171 . 2 


248 


216.7 


293 


262 .7 


7o 


38.1 


114 


82 .0 


159 


127 .O 


204 


172.2 


249 


217.7 


294 


263.7 


7i 


39.1 


115 


83.0 


160 


I28.O 


205 


173.2 


250 


218.8 


295 


264.7 


72 


40. 1 


116 


84.0 


161 


I29.O 


206 


174.2 


251 


219.8 


296 


265.7 


73 


41. 1 


H7 


85.0 


162 


I300 


207 


175.2 


252 


220.8 


297 


266.7 


74 


42.I 


118 


86.0 


163 


131 .O 


208 


176.2 


253 


221 .8 


298 


2678 


75 


43- 1 


119 


87.0 


164 


I32.0 


209 


177.2 


254 


222.8 


299 


268.8 






120 


88.0 


165 


I33-0 


210 


178.3 


255 


223.8 


300 


269.8 



VOLUME AND WEIGHT OF DISTILLED WATER. 



Temp. 


Weight of a 


Temp 


Weight of a 


Temp. 


Weight of a 


Degrees 


Cubic Foot 


Degrees 


Cubic Foot 


Degrees 


Cubic Foot 


Fahr. 


in Pounds. 


Fahr. 


in Pounds. 


Fahr. 


in Pounds. 


32 


62.417 


90 


62.110 


160 


61 .007 


391 


62 .425 


100 


62 .000 


170 


60 . 801 


40 


62.423 


no 


61 .867 


180 


60.587 


50 


62 .409 


120 


61 . 720 


190 


60.366 


60 


62.367 


130 


61.556 


200 


60. 136 


70 


62 .302 


140 


61.388 


210 


59894 


80 


62.218 


150 


61 .204 


212 


59.707 



APPENDIX. 
PROPERTIES OF SATURATED STEAM. 



5 2 7 



Pressure 
Pounds 

per 

Square 

Inch. 


Temperature 
Degrees F. 


Heat of 

Liquid 

above 32 . 


Heat of 

Vaporization 

or Total Latent 

Heat. 


Heat Contents 

above Water 

at 32 F. 


Volume in 
Cubic Feet 

of 
One Pound. 


5 


162.3 


I30.3 


IOOO. 


II30-3 


78.3 


IO 


193 


. 2 


161. 3 


981 


•4 


II42 


7 


38.4 


15 


213 


.0 


181. 3 


969 


1 


1150 


4 


26.3 


20 


227 


9 


196.4 


959 


4 


"55 


8 


20. 1 


25 


240 


. 1 


208.7 


95i 


4 


1 160 


1 


16.3 


30 


250 


•3 


219. 1 


944 


4 


1 163 


5 


13-7 


35 


259 


•3 


228. 2 


938 


2 


1 166 


4 


11. 9 


40 


267 


■3 


236.4 


932 


6 


1 169 





10.5 


45 


274 


5 


243-7 


927 


5 


1171 


2 


9-39 


50 


281 





250.4 


922 


8 


"73 


2 


8-51 


55 


287 


1 


256.6 


918 


4 


"75 





7-78 


60 


292 


7 


262 .4 


914 


3 


1 1 76 


7 


7.17 


65 


298 





267.8 


910 


4 


1178 


2 


6.65 


70 


303 





272.9 


906 


6 


"79 


5 


6.20 


75 


307 


6 


277.7 


903 


1 


1 180 


8 


S-81 


80 


312 


1 


282 . 2 


899 


8 


1182 





5-47 


85 


316 


3 


286.5 


896 


6 


1 183 


1 


5-i6 


90 


320 


3 


290.7 


893 


5 


1 184 


2 


4.89 


95 


324 


2 


294.6 


890 


5 


"85 


1 


4.64 


100 


327 


9 


298.5 


887 


6 


1 186 


1 


4-43 


105 


331 


4 


302.1 


884 


8 


1 186 


9 


4-23 


no 


334 


8 


305 .6 


882 


1 


1187 


1 


405 


ii5 


338 


1 


309.0 


879 


5 


1 188 


-5 


3-^ 


120 


34i 


3 


312.3 


876 


9 


1 189 


. 2 


3-72 


125 


344 


4 


315-5 


874 


5 


1 190 


.0 


3.58 


130 


347 


4 


318.6 


872 


1 


1 190 


•7 


3-45 


135 


35o 


3 


3215 


869 


8 


1191 


•3 


3-33 


140 


353 


1 


3244 


867 


4 


1191 


.8 


3-22 


145 


355 


8 


327-3 


865 


2 


1192 


•5 


3.12 


150 


358 


5 


330-° 


863 





"93 


.0 


3.01 


155 


361 


1 


332.7 


860 


9 


"93 


.6 


2.92 


160 


363 


6 


335-3 


858 


8 


1 194 


. 1 


2.83 


165 


366 


1 


337-9 


856 


8 


"94 


-7 


2-75 


170 


368 


5 


340.4 


854 


8 


"95 


. 2 


2.67 


175 


37o 


9 


342.8 


852 


8 


"95 


.6 


2.60 


180 


373 


2 


345-2 


850 


9 


1 196 


1 


2-53 


185 


375 


4 


347-5 


849 





1196 


5 


2-47 


190 


377 


6 


349-8 


847 


i 


iiq6 


9 


2.41 


195 


379 


8 


352.1 


845 


3 


"97 


4 


2.36 


200 


381 


9 


354-3 


843 


5 


"97 


8 


2. 29 


205 


384 





356-4 


841 


7 


1 198 


1 


2.24 


210 


386 





358.6 


840 





1198 


6 


2.18 


215 


388 





360.6 


838 


3 


1198 


9 


214 


220 


390 





362.7 


836 


6 


"99 


3 


2.09 


225 


39i 


9 


364-7 


834 


9 


"99 


6 


2.04 


230 


393 


8 


366.6 


833 


3 


"99 


9 


2.00 


235 


395- 


7 


368.6 


831. 


7 


1200 


3 


1 .96 


240 


397- 


5 


37o.5 


830. 


1 


1200. 


6 


1.92 


245 


399- 


3 


372.4 


828. 


5 


1200. 


9 


1.88 


250 


401 . 


1 


374-2 


826. 


9 


1201 . 


1 


1.85 



PLATE L 




PLATE II. 




LOCOMOTIVE BOILER 

160 LBS. PRESSURE 




SECTION THROUGH FIRE BOX REAR ELEVATION 




SECTION C-C LOOKING BACK- 



SECTION A-A LOOKING FRONT. 



108! 10 
SECTION B-B LOOKING FRONT. 



INDEX 



Page 

429 

Accumulators 

. 109 

Acetic acid , 

Adamson joints 

Air for combustion ' 9 

dilution 

, . . 181 

friction in pipes 

loss from excess 9 

per pound of coal 

supply for boiler, measurement of 455 

Almy boiler 33 

American independently-fired superheaters 45 

stoker 

Anchorage for pipes 377 

Angle- valves 3 

Anthracite coal 

Area, reduction of 

Area of circles 5 

378 
steam-pipe °' 

uptake 

Areas of segments of circles 52 ° 

Arrangement of induced draft * 91 

Artificial fuels 5 ° 

Ash-pit 

doors 

Ash, volume of ton of 74 

Assembling and riveting boilers 4 22 

Atmosphere, composition of 

Atomic weight ' ° 

Attached superheaters 39 

Babcock & Wilcox attached superheater 39 

boiler 22 

boiler setting x 33 

marine type 2 ? 

Back-pressure valve 35 

•D I20 

Ba g s „o 

Belleville boiler 25 

529 



530 INDEX 

Page 

Belt-conveyor 389, 394 

power required for 397 

Bending tests 256 

Bituminous coal 49 

Blow-off pipe 5, 367 

tanks 368 

Blowing out brine, loss from 126 

Blue heat 260 

Boiler accessories 326 

Almy 33 

assembling and riveting 422 

Babcock & Wilcox 22 

Belleville 28 

calculation of efficiency test of 459 

cold water test of 436 

Cornish 9 

design 468 

efficiency test of 45 7 

explosion of 319 

explosions, energy developed by 323 

fire engine 14 

general discussion of ^ 

graphic log sheet of test on 466 

horse power 218, 219 

Heine 24 

horizontal multitubular Plate I, 2, 3, 4 

hydraulic test to destruction 317 

Lancashire 7 

locomotive Plates II, III, 18, 20 

Manning 10, 1 1 

method of making evaporative test on 437 

plain cylindrical 7 

Scotch 15 

settings for, table of sizes 507 

shop arrangement of 409 

sizes of Babcock & Wilcox (table) 513 

Heine (table) 510 

horizontal tubular (table) 504 

Stirling (table) 509 

vertical (table) 508 

specifications and contract for 500 

Stirling 25 

testing 437 

Thornycroft 30 

thermal efficiency of 465 

two flue : 6 



INDEX 53 1 

Page 

Boiler, types of I 

vertical IO 

Yarrow 3 2 

Boilers, cost of 3° 

lap seam 3 2 4 

life of 320 

method of supporting 224 

ordinary proportions of 221 

strength of 249 

Boiler-plate, chemical determinations 256 

open hearth 255 

test specimen of 256 

Boiler-setting 129 

Babcock & Wilcox boiler 133 

cylindrical tubular boiler 130 

Heine boiler 134 

Stirling boiler 134 

Boiler-tubes, sizes of (table) 524 

Boring mill. 415 

Brace, diagonal 228 

Brackets, calculation of 499 

Brass 263 

Bridge wall 2 

Brine, loss from blowing out 126 

Bronze 263 

Bucket conveyor, power required by 393 

Butt-joint, double-riveted 282 

quadruple-riveted 285 

triple-riveted 283 

Calking 435 

Calorimeters 446 

Calorimeter tests 447 

Carbon, heat of combustion of 60 

monoxide, heat of combustion of 60 

Carbonic oxide, heat of combustion of 60 

Carbonate of lime in feed water 106 

soda in feed water 107 

Cast iron 261 

Channel-bar, layout of 494 

staying 225 

Charcoal 50 

Check valves 330 

Chemical determination of steel 256 

Chemistry of combustion 76 

Chimney, area 205 



532 INDEX 

Page 

Chimney, capacity 197 

draught 196 

calculations of 200 

needed 201 

temperature 198 

Chimneys 191 

cost of 196 

forms of 205 

radial brick 211 

stability of 206 

Kent's and Christie's (tables) 194, 195 

Circles, areas of 522 

Cleaning fires 168 

C0 2 recorders 96 

Sarco 99 

Uehling 96 

Coal bin — parabolic 401 

Coal, composition and heat of combustion of 51-58 

conveying apparatus 383 

cost of handling 393 

crushing 400 

handling 383 

handling and storing : . . . 401 

purchase of on specifications 70 

sampling 68 

specification, sample of 72 

tests, U. S. Geological survey 52-55 

valves 401 

volume of ton of 74 

weighing hoppers 405 

Coke 49 

Cold water test 436 

Combination 342 

Combustion, air required for ' 79 

chemistry of 76 

loss from incomplete 91 

rate of 219 

volume of air required for 82 

Complex stays 240 

Composition 263 

Composition and heat of combustion of coals 51 

foreign coals (Mahler) 58 

coals (Williams) 57 

coals (tables) 52-58 

Compression 254 

Conveyors, belt type 389, 394 



INDEX 533 

Page 

Conveyors, belt type, capacity and speed of 396 

capacity of flight 384 

Darley type 399 

Dodge type 388 

flight 383 

horse power of flight 384 

Hunt type 387 

McCaslin type 387 

Peck type 388 

pivoted bucket 385 

power to drive belt 397 

bucket 393 

size of belts 396 

Copper 262 

Cornish boiler 9 

Corrosion 122 

and incrustation 103 

prevention of 126 

Corrugated furnace 297 

Cost of boilers 36 

of chimneys 196 

Crane lifts 413 

Crow-foot staying 227 

Crude oil, heat of combustion of 59 

properties of 59 

Crushers for coal 400 

Crushing 274 

Crushing strength 274 

Cylinder, end tension of 267 

rim tension of 266 

thin hollow 266 

Cylindrical tubular boiler Plate I, 2 

setting 130 

staying of 223 

Damper regulator 348 

Darley conveyors 399 

Decomposition of steam 95 

Design of a boiler 468 

Determination of air per pound of coal 84 

Diagonal braces 228 

stays 265 

Dished heads 241 

Doors of water-legged boilers 237 

Double-riveted butt joint 282 

lap joint 277 



534 INDEX 

Page 

Double-riveted lap joint with inside cover plate 278 

Down-draught furnace 160 

Draught by fans 1 76 

Draught fans, induced or forced 176 

gauge 453 

Howden's system 168 

induced and forced 165 

required 201 

split 10 

wheel 9 

Dry pipe 242 

Dudgeon expander 433 

Dutch-oven furnace 138 

Dynamic head 179 

Economizers 169 

calculation of 174 

sizes of Green's (table) 515 

sizes of Sturtevant's (table) 516 

Efficiency of riveted joints 271 

Efficiency test of boiler 459 

calculation of 459 

Elastic limit 253 

Elasticity, modulus of 253 

Elements, atomic weights of 75 

End tension of cylinder 267 

Elongation, ultimate 254 

Explosions of boilers 319 

Equalizer 247 

Equivalent evaporation 216 

Evaporative test, sample of 457 

Excess air, loss from 92 

Factor of safety • 314 

Fans, calculation of induced draught 187 

for induced draught and for forced draught 176 

Farnley furnace 298 

Feed containing oil 115 

pipe 5, 359 

pump 360 

power type 363 

stage centrifugal 363 

Feed-water, analyses of (table) 104 

carbonate of lime in 106 

mineral impurities in 105 

organic impurities in 119 






index 535 

Page 

Feed-water, sulphate of lime in 106 

temperature of 443 

use of soda ash in 107 

use of tannic acid in 109 

Feed-water heaters 358 

lime extracting no 

Filter for oil 357 

removing oil from feed 115 

Fire cracks 168 

Fire-engine boiler 14 

Fire tubes 310 

Fires, cleaning 168 

Firing, methods of 143 

Fittings, bursting pressure of 376 

Flange punch 413 

Flanging 411 

Flat plates, strength of stayed 312 

Flight conveyors 383 

capacity of 384 

horse power of 384 

Flow of steam 451 

in pipes 379 

Napier's formula 332 

Rankine's formula 332 

Flue, area 205 

Flue gas analysis 85 

calculation of 88 

Flue gases, sampling of 452 

Flues 291 

rules for working pressure on 304 

strengthened 294 

tests of furnace 295 

Forced draught fans 176 

Forms of test piece 250 

Foster superheater 44 

Foundations 129 

Fox's corrugated furnace 297 

Friction of air in pipes 181 

Fuel oil, heat of combustion of 59 

properties of 59 

Furnace, Adamson type 309 

Brown type 308 

Farnley type 298 

Fox type 307 

flues, tests on 295 

Leed's bulb type 306 



536 INDEX 

Page 

Furnace, Morison type 302 

Purve's type 307 

short sections 308 

strength 306 

temperature hypothetical 94 

Furnaces 135 

down-draught 160 

Dutch oven 138 

Hawley down-draught 161 

Fusible plugs 346 

Gas analysis, calculation from a 88 

by Orsat apparatus 85 

Gases 50 

Gate valve 329 

Grate area 470 

General discussion of boilers 33 

Girders 310 

Globe valves 326 

Grate bars 140 

Grates, rocking 142 

Graphic log sheet 466 

Green traveling link grate 155 

Grooving 123 

Gun iron 261 

Gusset-stays ' 8, 241, 266 

Hand holes _. 244 

Hand riveting 431 

Hawley down-draught furnace 161 

Heat balance 463 

Heat of combustion 59 

calculation of 77 

determination of 60 

Dulong's formula 78 

Mahler's formula 79 

of coals 5 1-58 

crude oil 59 

fuel oil 59 

petroleum 59 

Heat of the liquid 526 

Heat of reaction 95 

Heater for extracting lime from feed water 110 

Heating surface 220 

relative value of 221 

Heine attached superheater 40 



INDEX 537 

Page 

Heine boiler 24 

boiler setting 134 

Holmes's furnace 299 

Homogeneity tests 257 

Horizontal multitubular boiler Plate I, 2, 3, 4 

Horse-power boiler rating 218 

Howden's system of draught 168 

Hunt conveyor 387 

Huston brace 230 

Hydrogen, heat of combustion of 60 

Incomplete combustion, loss from 91 

Independently fired superheater 44 

Induced draught fans 176 

arrangement of 190 

calculation of 187 

Induced draught fan and economizer 191 

Induced draught and forced draught 165 

Injectors 361 

Jacobs-Shupert fire-box 237 

Jones underfed stoker 155 

Kent's chimney sizes 194 

Kerosene and petroleum oils in feed water 122 

Laminations 259 

Lancashire boiler 7 

Lap 274, 482 

Lap-joint double-riveted 277 

inside cover plate 280 

single-riveted 275 

inside cover plate 278 

Lap seam boilers 324 

Leeds bulb furnace 306 

Lever safety valve 333 

Life of boilers 3 20 

Lifting dogs 412 

Lignite 49 

Lime-extracting feed-water heater no 

Locomotive boilers Plates II, III, 18, 20 

staying of 232 

Locomotive door frames 237 

pop safety valve 340 

Logarithms, table of 518 

Log sheet of boiler test 466 

Longitudinal joint 476 



538 INDEX 

Page 

Malleable iron 262 

Manholes 243 

Manning boiler 10, 1 1 

Marine boilers, staying of 238 

water tube 27 

type, Babcock and Wilcox 27 

water-tube boilers, settings of 135 

Marsh gas, heat of combustion of 60 

Material, methods of testing 251 

Mechanical stokers 144-158 

columns for building with 155 

Methods of supporting boilers 244 

testing material 251 

Mineral impurities in feed water , 105 

Mineral oil 50 

Modulus of elasticity 253 

Morison's furnace 302 

Murphy stoker 147 

Napier's formula 332 

Oil burners * . . 10 

filters 357 

filter for feed 115 

fuel 161 

scale 115 

Olefiant gas, heat of combustion of 60 

Open-hearth boiler plates 255 

Organic impurities in feed water 199 

Orsat's gas apparatus 85 

Pancake 118 

Parabola, area of 405 

Parabolic coal pocket 401 

Peat 49 

Petroleums, composition and heat of combustion of 59 

Pipe, blow-off 367 

covering 380 

joints, Van Stone 377 

methods of anchoring 377 

supporting 377 

Pipes, vibration of steam 376 

Pipe fittings, bursting strength of 376 

for superheated steam 47 

Piping 369 



INDEX 539 

Page 

Piping, elasticity of 373 

expansion of ' 369 

methods for allowing for expansion of 369 

Pitch 275 

Pitot tube 181 

Pitting 123 

Pivoted bucket carriers 385 

Plain flues, rules for 304 

Plate planers 4 J 8 

rolls 418 

Plates, drilled or punched 273 

tearing of 273 

Power pumps 363 

Pressure of steam 444 

Priming 445 

Proportion of rivets 269 

Prosser expander 432 

Pump for riveting 428 

Punch 418 

Punch and holder 414 

Purchase of coal on specifications 70 

Purve's furnace 300 

Pyrometers 454 

Quadruple-riveted butt joints 285 

Quality of steam 214 

Radial brick chimneys 211 

Rankine's formula 332 

Rate of combustion 219 

Reducing valve 347 

Reduction of area 254 

Resistance in flue passages 204 

Return steam trap 353 

Rim tension in cylinder 266 

Ringelmann smoke chart 158 

Ring seam 481 

Rivet, diameter of 275 

Rivet-heads, forms of 270 

Riveted joints 271 

designing of 287 

efficiency of 271 

friction of 274 

method of failure of 272 

practical considerations 291 

Riveting machine, portable 427 



54° INDEX 

Page 

Riveting machine, pump for 428 

Riveting machines 425 

Rivets 261 

pitch of 275 

proportion of 269 

shearing and crushing 274 

Rocking grates 142 

Rolls for plate -. 418 

Roney stoker 145 

Safety plugs 346 

Safety valves 331 

lever type 333 

calculation of 336 

locomotive pop 340 

pop type 337 

discharge of 332 

Sampling coal 68 

Sarco CO2 recorder 99 

Saturated steam, properties of (table) ' 527 

Scale from lime salts 106 

sea water 113 

Scarfing 418 

Scotch boilers 15 

Sea water, composition of : 112 

used in boilers 113 

Segmentof a circle, area of (table) 520 

Semi-anthracite coal 48 

Semi-bituminous coal 48 

Separators 355 

Setting for Babcock and Wilcox boiler 133 

Heine boiler 134 

horizontal multitubular boiler 130 

marine water-tube boiler 135 

Stirling boiler 134 

Shearing 254, 274 

plates . 417 

strength 274 

Shears for plate 417 

Shop practice 408 

Single-riveted lap joint 275 

inside cover plate 278 

Smoke chart, Ringelmann 158 

Smoke law for Metropolitan Boston 159 

Smoke prevention 157 

Snap riveting 431 

Soda-ash for feed water 108 



INDEX 541 

Page 

Soils, bearing pressure of 130 

Specific heat of substances (table) 75 

superheated steam 38 

Specifications and contract for boiler 500 

for purchase of coal 70 

steel 255 

Sphere, thin hollow 268 

Spherical ends 241 

Split draught 10 

Static head 1 79 

Stay bolts 263 

rods 493, 264 

calculation of 497 

Staying 491 

channel bar 225 

crow-feet 227 

cylindrical tubular boiler 223 

laying out of 491 

locomotive boilers 232 

marine boilers 238 

under tubes of back head 231 

vertical boilers 232 

with manhole in head 231 

Stays, diagonal 265 

gusset ' 266 

Steam 253 

decomposition of 95 

domes 242 

fittings for superheated 47 

flow in pipes 379 

flow of 451 

gauges 344 

meters 380 

nozzles 243 

pressure of 444 

quality of •. . . 214 

space 215, 471 

superheated 37 

Steam pipe, area of 378 

sizes of, table 525 

Steam pipes, vibration of : 376 

Steam separators 355 

Steam traps 350 

bucket type 351 

expansion type 353 

diaphragm type 352 



542 INDEX 

Page 

Steam traps, float type 350 

return type 355 

Steel specifications 254 

Still's curves for fans 180 

Stirling, attached superheater 45 

boiler 24 

setting 138 

Stokers, mechanical 144-159 

Strength of boilers 243 

ultimate 253 

Stress 253 

Submerged tube sheet 13, 14 

Sulphate of lime in feed water 106 

Sulphur, heat of combustion of 60 

Superheated steam 37 

pipe fittings for 47 

specific heat of 38 

Superheaters, attached 39~44 

Babcock and Wilcox 39 

Heine 40 

independently fired 44 _ 47 

Stirling 40 

Supports for boilers with stokers 155 

Tannic acid for feed water 109 

Taylor-Pitot tube 180 

Taylor stoker 149 

Temperature of furnace, hypothetical 94 

gases in chimney 198 

Test piece, forms of 250 

Testing machines 249 

Tests for bending 256 

homogeneity 257 

Thermal efficiency of a boiler 465 

Thickness of shell 476 

Thin hollow cylinder 266 

sphere 268 

Thornycrof t boiler 30 

Throttling calorimeter 446 

Trigonometric functions 522 

Triple-riveted butt-joints 283 

Tube cleaners 380 

expanders 432 

holes, drill for 414 

punch for 414 

sheet, layout of. 484 



INDEX 543 

Page 

Tube sheet, submerged 13, 14 

Tubes, sizes of (table) 524 

Turbine driven stage centrifugal feed pump 363 

Two-flue boiler 6 

Types of boilers 1 

Uehling C0 2 recorder 96 

Ultimate elongation 254 

strength 253 

Uptake, area of 487 

U. S. Geological Survey coal tests 52-55 

U. S. Inspectors, rules for flues 304 

Value of coal 214 

Valves, angle 328 

back-pressure 350 

check 330 

coal 401 

gate 329 

globe 326 

reducing 347 

safety 331 

Van Stone joints 377 

Vertical boiler 10, 11, 12 

Velocity head 179 

Vertical boilers, staying of 232 

Vibration in steam pipes 376 

Volume of air required for combustion 82 

ton of ash 74 

ton of coal 74 

Washout plugs 244 

Water column 342 

Water leg 18 

Water, volume of 526 

weight of 526 

Water-tube boilers 20-28 

marine boilers 27 

Weighing hoppers 405 

Wheel draught 9 

Wood 50 

Wrought iron 260 

Wrought-iron bars, weight of (table) 523 

Yarrow boiler 32 

Yield point 253, 255 



OCT 4 1912 



